Modifcations of general relativity generically contain additional degrees
of freedom that can mediate forces between matter particles. One of the
common manifestations of a ffth force in alternative gravity theories is
a diference between the gravitational potentials felt by relativistic and
non-relativistic particles, also known as ‘the gravitational slip’. In contrast,
a ffth force between dark matter particles, owing to dark sector interaction,
does not cause a gravitational slip, making the latter a possible ‘smoking
gun’ of modifed gravity. Here we point out that a force acting on dark matter
particles, as in models of coupled quintessence, would also manifest itself as
a measurement of an efective gravitational slip by cosmological surveys of
large-scale structure. This is linked to the fact that redshift-space distortions
owing to peculiar motion of galaxies do not provide a measurement of the
true gravitational potential if dark matter is afected by a ffth force. Hence,
it is extremely challenging to distinguish a dark sector interaction from a
modifcation of gravity with cosmological data alone. Future observations of
gravitational redshift from galaxy surveys can help to break the degeneracy
between these possibilities, by providing a direct measurement of the
distortion of time. We discuss this and other possible ways to resolve this
important question.
This document reviews research on the convergence of perturbation series in quantum field theory. It discusses Dyson's argument that perturbation series in quantum electrodynamics (QED) have zero radius of convergence due to vacuum instability when the coupling constant is negative. Large-order estimates show that perturbation series coefficients grow factorially fast in quantum mechanics and field theories. Finally, it describes the method of Borel summation, which may allow extracting the exact physical quantity from a divergent perturbation series through a unique mapping.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
While most of the singularities of General Relativity are expected to be safely hidden behind event horizons by the cosmic censorship conjecture, we happen to live in the causal future of the classical big bang singularity, whose resolution constitutes the active field of early universe cosmology...
The document discusses separating gravitational redshift from cosmic expansion redshift in observed cosmic microwave background radiation. It presents calculations of curvature ratios at different points in the early universe, such as at electroweak symmetry breaking and at the surface of last scattering. Taking the curvature ratio at these two points and using observed CMB redshift of 1091, the analysis estimates gravitational redshift would be around 2-3, with most of the observed redshift coming from cosmic expansion. This has implications for the energy density and relativistic nature of the early universe.
The document summarizes key aspects of the Standard Model of particle physics. It describes how the Standard Model accounts for fundamental particles like quarks and leptons that interact via four fundamental forces - gravitation, electromagnetism, weak force, and strong force. These interactions are mediated by exchange of spin-1/2 bosons. The Standard Model has been very successful in explaining experimental observations, but questions remain like incorporating gravity and the origin of particle masses.
Collective modes in the CFL phase - New Journal of Physics 13 (2011) 055002Roberto Anglani
This document summarizes a study of collective modes in the color flavor-locked (CFL) phase of dense quark matter. The authors derive the effective Lagrangian for the Nambu-Goldstone (NG) boson associated with spontaneous breaking of quark number symmetry, and determine corrections to previous results. They also derive the kinetic Lagrangian for the Higgs mode and interaction terms between the Higgs and NG fields using a Nambu-Jona-Lasinio model. This provides an effective description of low-energy excitations in the CFL phase to understand properties of compact stars containing quark matter.
This document reviews research on the convergence of perturbation series in quantum field theory. It discusses Dyson's argument that perturbation series in quantum electrodynamics (QED) have zero radius of convergence due to vacuum instability when the coupling constant is negative. Large-order estimates show that perturbation series coefficients grow factorially fast in quantum mechanics and field theories. Finally, it describes the method of Borel summation, which may allow extracting the exact physical quantity from a divergent perturbation series through a unique mapping.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
While most of the singularities of General Relativity are expected to be safely hidden behind event horizons by the cosmic censorship conjecture, we happen to live in the causal future of the classical big bang singularity, whose resolution constitutes the active field of early universe cosmology...
The document discusses separating gravitational redshift from cosmic expansion redshift in observed cosmic microwave background radiation. It presents calculations of curvature ratios at different points in the early universe, such as at electroweak symmetry breaking and at the surface of last scattering. Taking the curvature ratio at these two points and using observed CMB redshift of 1091, the analysis estimates gravitational redshift would be around 2-3, with most of the observed redshift coming from cosmic expansion. This has implications for the energy density and relativistic nature of the early universe.
The document summarizes key aspects of the Standard Model of particle physics. It describes how the Standard Model accounts for fundamental particles like quarks and leptons that interact via four fundamental forces - gravitation, electromagnetism, weak force, and strong force. These interactions are mediated by exchange of spin-1/2 bosons. The Standard Model has been very successful in explaining experimental observations, but questions remain like incorporating gravity and the origin of particle masses.
Collective modes in the CFL phase - New Journal of Physics 13 (2011) 055002Roberto Anglani
This document summarizes a study of collective modes in the color flavor-locked (CFL) phase of dense quark matter. The authors derive the effective Lagrangian for the Nambu-Goldstone (NG) boson associated with spontaneous breaking of quark number symmetry, and determine corrections to previous results. They also derive the kinetic Lagrangian for the Higgs mode and interaction terms between the Higgs and NG fields using a Nambu-Jona-Lasinio model. This provides an effective description of low-energy excitations in the CFL phase to understand properties of compact stars containing quark matter.
1. The document discusses global gravitational anomalies and transport coefficients arising from anomalies in quantum field theories.
2. It summarizes previous work relating anomalies to transport, and notes discrepancies for theories with chiral gravitinos.
3. The main focus is on using a global anomaly matching approach and constructing effective actions to understand the relationship between gravitational anomalies and transport coefficients for various theories in different dimensions, including theories with Weyl fermions and chiral gravitinos in d=2.
This document summarizes a talk on the variation of fundamental constants over time. It discusses several methods for measuring potential variations, including analyses of the cosmic microwave background, quasar absorption spectra, radioactive decay rates from the natural nuclear reactor at Oklo, and comparisons of atomic clock rates. Measurements from big bang nucleosynthesis and quasar data suggest the fine structure constant may have been smaller in the early universe, varying on the order of 10^-15 per year. However, results are not conclusive and depend on theoretical models. Ongoing work using improved atomic clocks aims to more precisely measure any drift of fundamental constants like the fine structure constant and quark-mass ratios over time.
Excitons, lifetime and Drude tail within the current~current response framew...Claudio Attaccalite
We compare the optical absorption of extended systems calculated starting from the density-density and current-current linear response formalisms within the equilibrium many-body perturbation theory(MBPT). We show how, using the latter, one can incur in errors due to quasiparticle lifetimes, electron-hole interaction or the presence of a Drude tail. We present a solution for each one of these problems.
- The document derives the second order Friedmann equations from the quantum corrected Raychaudhuri equation (QRE), which includes quantum corrections terms.
- One correction term can be interpreted as dark energy/cosmological constant with the observed density value, providing an explanation for the coincidence problem.
- The other correction term can be interpreted as a radiation term in the early universe that prevents the formation of a big bang singularity and predicts an infinite age for the universe by avoiding a divergence in the Hubble parameter or its derivative at any finite time in the past.
Using the Milky Way satellites to study interactions between cold dark matter...GOASA
The document discusses using simulations of cold dark matter (CDM) interacting with radiation (photons or neutrinos) to study its impact on the number of satellite galaxies around the Milky Way. It finds that including such interactions leads to a dramatic reduction in satellite galaxies that could help alleviate tensions between the CDM model and observations. The methodology allows stronger constraints on dark matter interactions than from cosmic microwave background data alone. Simulations of CDM interacting with photons show a reduced number of subhalos around Milky Way-sized halos for interaction cross sections allowed by CMB data, demonstrating this physics may be important for small-scale structure formation predictions.
Burin braneworld cosmological effect with induced gravityluciolucena
1) The document discusses braneworld cosmology models where our universe is a 3-dimensional brane embedded in extra dimensions. It analyzes the Friedmann equations for a brane with induced gravity and compares them to standard general relativity and Randall-Sundrum models.
2) In the Randall-Sundrum model, gravity is modified at early times whereas induced gravity affects late universe evolution. The document solves the Friedmann equations in various limits and regimes to understand the modifications to the standard cosmology dynamics.
3) It finds that induced gravity effects from the Dvali-Gabadadze-Porrati model can contribute to late-time acceleration of the universe expansion under certain
Grand unified field theory a predator prey approach corroboration dissipation...Alexander Decker
The document discusses the four fundamental interactions in nature: gravitation, electromagnetism, strong nuclear force, and weak nuclear force. It describes how each interaction is mediated by different bosons being exchanged between fermions. The strong nuclear force binds quarks together via gluon exchange. The document also discusses how gravitation, while the weakest force on small scales, becomes important on large macroscopic scales due to its infinite range and inability to be shielded against.
This document summarizes a presentation about reconstructing inflationary models in modified f(R) gravity. It discusses the current status of inflation based on Planck data, reviews how inflation works in f(R) gravity, and describes two approaches - the direct approach of comparing models to data and the inverse approach of smoothly reconstructing models from observational quantities like the scalar spectrum index. A key model discussed is the simple R + R^2 model that can match current measurements of the spectral index and tensor-to-scalar ratio.
This document summarizes a research project that involves building a toy model of particle collisions using C++ and ROOT. The model simulates collisions by sampling probability distributions measured in real collisions. It generates particles and assigns them properties like momentum and angle. It also models physical processes like jet production and elliptic flow. The goal is to study how properties of particles like jets are affected by a quark-gluon plasma and vice versa. The model allows tuning parameters to learn about collision interactions and switch physics processes on or off.
This is a "post-preprint" of a contributed paper at the XXII International conference on High Energy Physics Leipzig, July 19-25, 1984. Some of the ideas developed in this paper may turn out to be useful in the interpretation of the standard model of modern cosmology
This is a post-preprint of a contributed paper at the XXII International conference on High Energy Physics Leipzig, July 19-25, 1984. Some of the ideas developed in this paper may be useful in the interpretation of the standard model of modern cosmology
This document summarizes a study that uses distance measurements in the nearby universe to test theories of modified gravity. The study compares distance measurements from cepheid variable stars, tip of the red giant branch stars, and water masers in different galaxies. These distance indicators operate in gravitational fields of different strengths, enabling tests of scalar-tensor gravity theories where fifth forces are screened to different extents depending on the local gravitational potential. The study finds no evidence for the enhanced gravitational forces predicted by chameleon and symmetron screening scenarios, constraining the parameter space of these theories.
Direct detection of ultralight dark matter bound to the Sun with space quantu...Sérgio Sacani
Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock and the Parker Solar Probe, we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If a two-clock system were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter, which couples to electron, photon and gluon fields, based on current and future atomic, molecular and nuclear clocks
This document is a project report submitted by Shubham Patel for the partial fulfillment of an M.Sc. in Physics. The report introduces Galilean electromagnetism and constrained Hamiltonian systems. In part one, the report discusses various Galilean limits of Maxwell's equations including the electric limit, magnetic limit, and Carrollian limit. It also discusses formulations of these limits that are invariant under different systems of units. In part two, the report discusses Maxwell's field theory from a Hamiltonian perspective and constraints that arise in the formulation. It also discusses a higher order field tensor Lagrangian and its Hamiltonian formulation.
Dark Matter Annihilation inside Large-Volume Neutrino DetectorsSérgio Sacani
New particles in theories beyond the standard model can manifest as stable relics that interact strongly with visible matter and make up a small fraction of the total dark matter abundance. Such particles represent an interesting physics target since they can evade existing bounds from direct detection due to their rapid thermalization in high-density environments. In this work we point out that their annihilation to visible matter inside large-volume neutrino telescopes can provide a new way to constrain or discover such particles. The signal is the most pronounced for relic masses in the GeV range, and can be efficiently constrained by existing Super-Kamiokande searches for dinucleon annihilation. We also provide an explicit realization of this scenario in the form of secluded dark matter coupled to a dark photon, and we show that the present method implies novel and stringent bounds on the model that are complementary to direct constraints from beam dumps, colliders, and direct detection experiments.
Quantum-Gravity Thermodynamics, Incorporating the Theory of Exactly Soluble Active Stochastic Processes, with Applications
by Daley, K.
Published in IJTP in 2009. http://adsabs.harvard.edu/abs/2009IJTP..tmp...67D
Zvonimir Vlah "Lagrangian perturbation theory for large scale structure forma...SEENET-MTP
This document discusses using Lagrangian perturbation theory and the effective field theory (EFT) approach to model large-scale structure (LSS) formation, including nonlinear effects. Key points include:
- The Lagrangian framework tracks fluid elements as they move due to gravity, described by a displacement field. This allows modeling of shell crossing nonlinearities.
- The EFT approach introduces a stress tensor to account for short-distance effects on long-wavelength modes. Counterterms are included to absorb uncertainties from neglected short-scale physics.
- Power spectrum and correlation function results from the Lagrangian EFT approach match those of the standard Eulerian EFT approach. The Lagrangian approach provides insights into counterterm structures and infrared resummation
This study investigated Z' and Z'' bosons in the Minimal Walking Technicolor model by combining theoretical predictions with experimental data from the CMS experiment. The authors calculated cross sections for Z' and Z'' production and decay in the di-lepton channel across a parameter space of MA and g-tilde, which define the mass scale and coupling of these new particles. Regions where theoretical cross sections exceeded experimental limits were excluded, providing the first combined exclusion limits for this WTC model and improving on previous parameter space constraints. A statistical analysis of potential Z' and Z'' resonance peaks further strengthened the excluded region.
- The document discusses a braneworld model where a 3-brane moves in a 5-dimensional anti-de Sitter bulk. The brane behaves effectively as a tachyon field with an inverse quartic potential.
- When the backreaction of the radion field (related to fluctuations of the brane position) is included, the tachyon Lagrangian is modified by its interaction with the radion. This results in an effective equation of state at large scales that describes "warm dark matter".
- The model extends the second Randall-Sundrum braneworld model to include nonlinear effects from the radion field, which distorts the anti-de Sitter geometry.
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
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Similar a Modified Einstein versus modified Euler for dark matter
1. The document discusses global gravitational anomalies and transport coefficients arising from anomalies in quantum field theories.
2. It summarizes previous work relating anomalies to transport, and notes discrepancies for theories with chiral gravitinos.
3. The main focus is on using a global anomaly matching approach and constructing effective actions to understand the relationship between gravitational anomalies and transport coefficients for various theories in different dimensions, including theories with Weyl fermions and chiral gravitinos in d=2.
This document summarizes a talk on the variation of fundamental constants over time. It discusses several methods for measuring potential variations, including analyses of the cosmic microwave background, quasar absorption spectra, radioactive decay rates from the natural nuclear reactor at Oklo, and comparisons of atomic clock rates. Measurements from big bang nucleosynthesis and quasar data suggest the fine structure constant may have been smaller in the early universe, varying on the order of 10^-15 per year. However, results are not conclusive and depend on theoretical models. Ongoing work using improved atomic clocks aims to more precisely measure any drift of fundamental constants like the fine structure constant and quark-mass ratios over time.
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We compare the optical absorption of extended systems calculated starting from the density-density and current-current linear response formalisms within the equilibrium many-body perturbation theory(MBPT). We show how, using the latter, one can incur in errors due to quasiparticle lifetimes, electron-hole interaction or the presence of a Drude tail. We present a solution for each one of these problems.
- The document derives the second order Friedmann equations from the quantum corrected Raychaudhuri equation (QRE), which includes quantum corrections terms.
- One correction term can be interpreted as dark energy/cosmological constant with the observed density value, providing an explanation for the coincidence problem.
- The other correction term can be interpreted as a radiation term in the early universe that prevents the formation of a big bang singularity and predicts an infinite age for the universe by avoiding a divergence in the Hubble parameter or its derivative at any finite time in the past.
Using the Milky Way satellites to study interactions between cold dark matter...GOASA
The document discusses using simulations of cold dark matter (CDM) interacting with radiation (photons or neutrinos) to study its impact on the number of satellite galaxies around the Milky Way. It finds that including such interactions leads to a dramatic reduction in satellite galaxies that could help alleviate tensions between the CDM model and observations. The methodology allows stronger constraints on dark matter interactions than from cosmic microwave background data alone. Simulations of CDM interacting with photons show a reduced number of subhalos around Milky Way-sized halos for interaction cross sections allowed by CMB data, demonstrating this physics may be important for small-scale structure formation predictions.
Burin braneworld cosmological effect with induced gravityluciolucena
1) The document discusses braneworld cosmology models where our universe is a 3-dimensional brane embedded in extra dimensions. It analyzes the Friedmann equations for a brane with induced gravity and compares them to standard general relativity and Randall-Sundrum models.
2) In the Randall-Sundrum model, gravity is modified at early times whereas induced gravity affects late universe evolution. The document solves the Friedmann equations in various limits and regimes to understand the modifications to the standard cosmology dynamics.
3) It finds that induced gravity effects from the Dvali-Gabadadze-Porrati model can contribute to late-time acceleration of the universe expansion under certain
Grand unified field theory a predator prey approach corroboration dissipation...Alexander Decker
The document discusses the four fundamental interactions in nature: gravitation, electromagnetism, strong nuclear force, and weak nuclear force. It describes how each interaction is mediated by different bosons being exchanged between fermions. The strong nuclear force binds quarks together via gluon exchange. The document also discusses how gravitation, while the weakest force on small scales, becomes important on large macroscopic scales due to its infinite range and inability to be shielded against.
This document summarizes a presentation about reconstructing inflationary models in modified f(R) gravity. It discusses the current status of inflation based on Planck data, reviews how inflation works in f(R) gravity, and describes two approaches - the direct approach of comparing models to data and the inverse approach of smoothly reconstructing models from observational quantities like the scalar spectrum index. A key model discussed is the simple R + R^2 model that can match current measurements of the spectral index and tensor-to-scalar ratio.
This document summarizes a research project that involves building a toy model of particle collisions using C++ and ROOT. The model simulates collisions by sampling probability distributions measured in real collisions. It generates particles and assigns them properties like momentum and angle. It also models physical processes like jet production and elliptic flow. The goal is to study how properties of particles like jets are affected by a quark-gluon plasma and vice versa. The model allows tuning parameters to learn about collision interactions and switch physics processes on or off.
This is a "post-preprint" of a contributed paper at the XXII International conference on High Energy Physics Leipzig, July 19-25, 1984. Some of the ideas developed in this paper may turn out to be useful in the interpretation of the standard model of modern cosmology
This is a post-preprint of a contributed paper at the XXII International conference on High Energy Physics Leipzig, July 19-25, 1984. Some of the ideas developed in this paper may be useful in the interpretation of the standard model of modern cosmology
This document summarizes a study that uses distance measurements in the nearby universe to test theories of modified gravity. The study compares distance measurements from cepheid variable stars, tip of the red giant branch stars, and water masers in different galaxies. These distance indicators operate in gravitational fields of different strengths, enabling tests of scalar-tensor gravity theories where fifth forces are screened to different extents depending on the local gravitational potential. The study finds no evidence for the enhanced gravitational forces predicted by chameleon and symmetron screening scenarios, constraining the parameter space of these theories.
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Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock and the Parker Solar Probe, we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If a two-clock system were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter, which couples to electron, photon and gluon fields, based on current and future atomic, molecular and nuclear clocks
This document is a project report submitted by Shubham Patel for the partial fulfillment of an M.Sc. in Physics. The report introduces Galilean electromagnetism and constrained Hamiltonian systems. In part one, the report discusses various Galilean limits of Maxwell's equations including the electric limit, magnetic limit, and Carrollian limit. It also discusses formulations of these limits that are invariant under different systems of units. In part two, the report discusses Maxwell's field theory from a Hamiltonian perspective and constraints that arise in the formulation. It also discusses a higher order field tensor Lagrangian and its Hamiltonian formulation.
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New particles in theories beyond the standard model can manifest as stable relics that interact strongly with visible matter and make up a small fraction of the total dark matter abundance. Such particles represent an interesting physics target since they can evade existing bounds from direct detection due to their rapid thermalization in high-density environments. In this work we point out that their annihilation to visible matter inside large-volume neutrino telescopes can provide a new way to constrain or discover such particles. The signal is the most pronounced for relic masses in the GeV range, and can be efficiently constrained by existing Super-Kamiokande searches for dinucleon annihilation. We also provide an explicit realization of this scenario in the form of secluded dark matter coupled to a dark photon, and we show that the present method implies novel and stringent bounds on the model that are complementary to direct constraints from beam dumps, colliders, and direct detection experiments.
Quantum-Gravity Thermodynamics, Incorporating the Theory of Exactly Soluble Active Stochastic Processes, with Applications
by Daley, K.
Published in IJTP in 2009. http://adsabs.harvard.edu/abs/2009IJTP..tmp...67D
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This document discusses using Lagrangian perturbation theory and the effective field theory (EFT) approach to model large-scale structure (LSS) formation, including nonlinear effects. Key points include:
- The Lagrangian framework tracks fluid elements as they move due to gravity, described by a displacement field. This allows modeling of shell crossing nonlinearities.
- The EFT approach introduces a stress tensor to account for short-distance effects on long-wavelength modes. Counterterms are included to absorb uncertainties from neglected short-scale physics.
- Power spectrum and correlation function results from the Lagrangian EFT approach match those of the standard Eulerian EFT approach. The Lagrangian approach provides insights into counterterm structures and infrared resummation
This study investigated Z' and Z'' bosons in the Minimal Walking Technicolor model by combining theoretical predictions with experimental data from the CMS experiment. The authors calculated cross sections for Z' and Z'' production and decay in the di-lepton channel across a parameter space of MA and g-tilde, which define the mass scale and coupling of these new particles. Regions where theoretical cross sections exceeded experimental limits were excluded, providing the first combined exclusion limits for this WTC model and improving on previous parameter space constraints. A statistical analysis of potential Z' and Z'' resonance peaks further strengthened the excluded region.
- The document discusses a braneworld model where a 3-brane moves in a 5-dimensional anti-de Sitter bulk. The brane behaves effectively as a tachyon field with an inverse quartic potential.
- When the backreaction of the radion field (related to fluctuations of the brane position) is included, the tachyon Lagrangian is modified by its interaction with the radion. This results in an effective equation of state at large scales that describes "warm dark matter".
- The model extends the second Randall-Sundrum braneworld model to include nonlinear effects from the radion field, which distorts the anti-de Sitter geometry.
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Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
PPT on Alternate Wetting and Drying presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
ESA/ACT Science Coffee: Diego Blas - Gravitational wave detection with orbita...Advanced-Concepts-Team
Presentation in the Science Coffee of the Advanced Concepts Team of the European Space Agency on the 07.06.2024.
Speaker: Diego Blas (IFAE/ICREA)
Title: Gravitational wave detection with orbital motion of Moon and artificial
Abstract:
In this talk I will describe some recent ideas to find gravitational waves from supermassive black holes or of primordial origin by studying their secular effect on the orbital motion of the Moon or satellites that are laser ranged.
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
Mending Clothing to Support Sustainable Fashion_CIMaR 2024.pdfSelcen Ozturkcan
Ozturkcan, S., Berndt, A., & Angelakis, A. (2024). Mending clothing to support sustainable fashion. Presented at the 31st Annual Conference by the Consortium for International Marketing Research (CIMaR), 10-13 Jun 2024, University of Gävle, Sweden.
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Modified Einstein versus modified Euler for dark matter
1. Nature Astronomy
natureastronomy
https://doi.org/10.1038/s41550-023-02003-y
Analysis
ModifiedEinsteinversusmodifiedEulerfor
darkmatter
Camille Bonvin 1
& Levon Pogosian2
Modificationsofgeneralrelativitygenericallycontainadditionaldegrees
offreedomthatcanmediateforcesbetweenmatterparticles.Oneofthe
commonmanifestationsofafifthforceinalternativegravitytheoriesis
adifferencebetweenthegravitationalpotentialsfeltbyrelativisticand
non-relativisticparticles,alsoknownas‘thegravitationalslip’.Incontrast,
afifthforcebetweendarkmatterparticles,owingtodarksectorinteraction,
doesnotcauseagravitationalslip,makingthelatterapossible‘smoking
gun’ofmodifiedgravity.Herewepointoutthataforceactingondarkmatter
particles,asinmodelsofcoupledquintessence,wouldalsomanifestitselfas
ameasurementofaneffectivegravitationalslipbycosmologicalsurveysof
large-scalestructure.Thisislinkedtothefactthatredshift-spacedistortions
owingtopeculiarmotionofgalaxiesdonotprovideameasurementofthe
truegravitationalpotentialifdarkmatterisaffectedbyafifthforce.Hence,
itisextremelychallengingtodistinguishadarksectorinteractionfroma
modificationofgravitywithcosmologicaldataalone.Futureobservationsof
gravitationalredshiftfromgalaxysurveyscanhelptobreakthedegeneracy
betweenthesepossibilities,byprovidingadirectmeasurementofthe
distortionoftime.Wediscussthisandotherpossiblewaystoresolvethis
importantquestion.
The discovery of cosmic acceleration1,2
and the unknown nature
of dark matter (DM) prompted extensive studies of modified
gravity theories. Generically3,4
, such theories involve, in addition to
themetrictensor,newdynamicaldegreesoffreedom,withascalarfield
being the most commonly studied example5,6
. In these scalar-tensor
theories, gravitational attraction between matter particles is
mediated by the curvature of spacetime as well as the scalar field.
At the level of linear cosmological perturbations, this ‘fifth force’
not only enhances the rate of gravitational clustering of matter but
also manifests itself as a non-zero ‘gravitational slip’7,8
, namely, a
difference between the Newtonian potential Ψ and the curvature
perturbation Φ. One can search for evidence of Ψ ≠ Φ by combining
observations of galaxy redshift-space distortions (RSDs) and weak
gravitational lensing (WL), along with other cosmological data9–11
. A
measurement of Φ ≠ Ψ is often considered to be the ‘smoking gun’ of
modified gravity.
What if instead of having modifications of gravity affecting all
matter, only the DM particles experience an attractive force owing to
some non-gravitational dark sector interaction? Can cosmological
observationsdistinguishadarksectorforce,thataffectsonlyDM,from
amodificationofgravitythataltersgravityforallmatter?Phrasingitin
mathematicalterms,canonedistinguishamodificationoftheEinstein
equations from a modification of the Euler equation for DM? While
findinganyevidenceofafifthforcewouldbeofprofoundimportance
by itself, knowing whether it is of gravitational or particle origin is an
equallyfundamentalquestion.
This question is not new and has been discussed, for example, in
thecontextofscalar-fielddarkenergy12,13
.Aminimallycoupledscalar
field is usually referred to as quintessence14,15
, whereas a scalar field
coupledonlytoDMwouldbeclassifiedascoupledquintessence(CQ).
(Notethatintheearlierliterature,forexample,ref.16,thetermCQwas
also used to refer to coupling to all matter, but in more recent years
Received: 3 October 2022
Accepted: 15 May 2023
Published online: xx xx xxxx
Check for updates
1
Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, Geneva, Switzerland. 2
Department of Physics,
Simon Fraser University, Burnaby, British Columbia, Canada. e-mail: camille.bonvin@unige.ch
2. Nature Astronomy
Analysis https://doi.org/10.1038/s41550-023-02003-y
densitycontrasts,δb = δρb/ρb andδc = δρc/ρc,(hereδρdenotesthelinear
perturbation of the energy density ρ) and their velocity divergences,
θb and θc. As shown in Methods, in both GBD and CQ, the equations
governing the evolution of these variables can be combined into an
evolution equation for the matter density contrast
̈
δ + ℋ ̇
δ = 4πGeffa2
ρ δ , (4)
where the overdots denote derivatives with respect to τ, ℋ is the
Hubble parameter in conformal time, ρδ = ρcδc + ρbδb, and Geff is the
effective gravitational coupling that takes the following forms
GGBD
eff
= G [1 +
2 ̃
β2k2
a2m2+k2
] and GCQ
eff
= G [1 +
2 ̃
β2k2
a2m2+k2
(
ρc
ρ
)
2
(
δc
δ
)] ,
(5)
where ̃
β2
= β2
/8πG, β = A,ϕ/A is the scalar-field coupling strength and
m2
istheeffectivemassthatsetstherangeofthefifthforce.Weseethat
theeffectivegravitationalcouplingsareverysimilarinthetwomodels.
The only difference is a small suppression of the impact of the fifth
force in GCQ
eff
, owing to the fact that ~15% of matter does not feel the
fifth force. This difference is, however, degenerate with the unknown
coupling ̃
β. We see, therefore, that GBD and CQ are impossible to
distinguishthroughthegrowthofstructurealone.Anobserverlooking
for departures from the Λ cold dark matter model (where Λ is the
cosmological constant) by fitting Geff to the galaxy growth data (for
example, using MGCAMB20
) would measure a Geff > 1 either way. Note
that the argument derived here in the case of a scalar field holds
in general: modifications to the Poisson equation (due to modified
gravity) and modifications to the Euler equation (due to a dark fifth
force)aregenericallyindistinguishableatthelevelofthegrowthrate21
,
which is the quantity measured by RSD.
However, the two types of theory differ at the level of the gravi-
tational potentials. In GBD, the two potentials differ, Φ ≠ Ψ, hence
η ≡ Φ/Ψ ≠ 1,whereasinCQtheEinsteinequationsarenotmodified,and
therefore,atlatetimes,η = 1.Thissuggeststhatonecoulddifferentiate
thetwocasesbymeasuringη(refs.13,19),makingitasmokinggunfor
modifiedgravity.Notethatmodifiedgravityeffectsonlinearperturba-
tionscan,inprinciple,bemimickedbyadarkfluidwithappropriately
tunedstatefunctions(see,forexample,refs.22,23).Here,ratherthan
aiming to distinguish between a modified gravity and a hypothetical
fluid, we compare a modified gravity in which a fifth force affects all
matter with a theory in which the same type of force acts only on DM,
withnoadditionaldarkingredients.
In practice, deviations from general relativity are often para
meterized with two functions μ and Σ that depend on a and on the
wavenumber k
k2
Ψ = −4πμ(a, k)Ga2
ρ δ , (6)
k2
(Φ + Ψ) = −8πΣ(a, k)Ga2
ρ δ , (7)
where, in GBD
μ =
GGBD
eff
G
and Σ =
1
2
μ(1 + η) = 1 , (8)
whileinCQ,μ = Σ = η = 1.Intheory,combiningameasurementofbaryon
velocities, determined by the Newtonian potential Ψ, with WL data
that measure Φ + Ψ, would yield a measurement of both μ and Σ and,
therefore, determine η. However, as we show below, this test would
not work in practice because the baryons we observe are confined to
galaxiesand,hence,movetogetherwiththegalacticDM.Thismeansan
observerwouldmeasureaneffectiveηfit
≠ 1evenifthereisnointrinsic
gravitational slip.
CQ has been generally used to refer to the DM-only coupled case13,17
.)
In contrast, a scalar field universally coupled to all matter would be
referred to as a scalar-tensor theory12,13
and, hence, considered to
be modified gravity. Several publications have suggested that a way
to differentiate between CQ and scalar-tensor gravity would be to
measure the gravitational slip12,13,18,19
. This expectation, however,
relies on our ability to measure the perturbation of the velocity field
of the normal matter (‘baryons’) and use it to infer the underlying
large-scale Ψ.
In this Analysis, we argue that this is not possible with current
observations.Thereasonisthatthebaryonsweobserveareconfined
ingalaxiesandclusters.Assuchtheirvelocityislinkedtothevelocityof
galaxiesand,therefore,theydonottracethelarge-scaleΨ,ifDMexpe-
riences a fifth force. The effective Newtonian potential inferred from
RSDs, when compared with WL measurements, would consequently
yield a non-zero measured gravitational slip indistinguishable from
thatcomingfrommodifiedgravity.
Fortunately, the next generation of large-scale structure surveys
has the potential to break this degeneracy between modified gravity
andadarkforceactingonDM(hereaftercalleddarkforce),byproviding
a measurement of the distortion of time. This novel observable has
the advantage of being directly sensitive to Ψ, even in the presence
ofadarkforce.
Thesmokinggunargument
We start by comparing two models: a scalar-tensor theory of general-
ized Brans–Dicke (GBD) type and a CQ model. While the equations
of motion and the perturbations we show are specific to these two
models, the argument is general and holds for any modified gravity
theory and dark force model.
TheactionforGBDtakestheform
SGBD
= ∫ d4
√−g [
A−2
(ϕ)
16πG
R −
1
2
∂μϕ ∂μ
ϕ − V(ϕ) + ℒm(ψDM, ψSM, gμν)] ,
(1)
whereGistheNewtonconstant,RistheRicciscalarbuiltfromgμν and
its derivatives, g is the metric determinant, A is a generic function
of the scalar field 𝜙 and V is its potential. ℒm(ψDM, ψSM, gμν) is the
Lagrangiandensityofallmatterthatincludesthestandardmodel(SM)
particle fields, collectively denoted as ψSM, and the DM particles,
denoted as ψDM, with both following the geodesics of the metric gμν.
Throughoutthispaper,gμν denotesthemetricofthe‘baryonframe’,that
is,themetricwhosegeodesicsarefollowedbytheSMparticles(which,
inthecaseofthescalar-tensortheories,isthesameforbaryonsandDM).
Let us compare the GBD action (equation ((1)) with the action of
CQ,withthescalarfieldconformallycoupledonlytoDM
SCQ
= ∫ d4
√−g[
1
16πG
R −
1
2
∂μϕ ∂μ
ϕ − V(ϕ)
+ ℒSM(ψSM, gμν) + ℒDM(ψDM, A2
(ϕ)gμν)],
(2)
in which the gravitational part of the action is not modified in the
baryon frame gμν, and with DM following geodesics of A2
(ϕ)gμν.
We always interpret the observations in the ‘baryon frame’, in
which the masses of the SM particles are constant. With that in mind,
let us compare the equations governing linear cosmological pertur-
bations in GBD and CQ theories. We work with the linearly perturbed
flat Friedmann–Lemaître–Robertson–Walker (FLRW) metric in the
conformalNewtoniangauge,withthelineelementgivenby
ds2
= gμνdxμ
dxν
= a2
(τ) [−(1 + 2Ψ)dτ2
+ (1 − 2Φ)dx2
] , (3)
where τ denotes conformal time and a is the scale factor. Neglecting
radiation, the relevant variables are Ψ, Φ, the baryon and (cold) DM
3. Nature Astronomy
Analysis https://doi.org/10.1038/s41550-023-02003-y
Theobservedgravitationalslip
To understand how the gravitational slip is measured from RSDs
and WL, let us first review how these observables are constructed.
Redshift surveys map the distribution of galaxies and measure the
fluctuation in the galaxy number counts, given in Fourier space by
Δ(k, z) = δg(k, z) −
1
ℋ
μ2
k
θb(k, z) , (9)
wherezistheredshift, μk = ̂
k ⋅ n,andnisthedirectionofobservation
(considered fixed in the flat-sky approximation). The first term is
the intrinsic fluctuation in the distribution of galaxies δg, related
to the (total) matter density contrast through the bias b: δg = bδ.
The second term is due to RSDs24
, accounting for the fact that the
redshift of the galaxies is affected by the peculiar velocity of the
baryons (from which the light that we receive is emitted) with
respect to us. As shown in Methods, the velocity of baryons can
be decomposed into two terms: the velocity of the baryons with
respecttothecentreofmassofthegalaxy,andthegalacticcentre-of-
mass velocity with respect to the Hubble flow. These two terms are
sensitive to different ingredients. As illustrated in Fig. 1, the velocity
of the baryons with respect to the centre of mass is governed by the
local gravitational potential of the galaxy, whereas the velocity of
the centre of mass is driven by the large-scale gravitational potential.
As RSD surveys measure correlations of galaxy number counts at
large separations (well above the size of a galaxy), the first velocity
contribution vanishes, since it is not correlated on large scales.
Consequently,theRSDpowerspectrumisaffectedbyonlythemotion
of the galactic centre of mass, and we can effectively replace θb in
equation(9)bythecentre-of-massvelocity,denotedbyθg.InGBD,the
centreofmassmovesaccordingtothelarge-scalegravitationalpoten-
tial ΨLS
. In the CQ model however, the centre-of-mass velocity is also
affected by the fifth force:
GBD ∶ ̇
θg + ℋθg = k2
ΨLS
, (10)
CQ ∶ ̇
θg + ℋθg = k2
ΨLS
+
ρc
ρ
k2
βδϕ ≡ k2
Ψeff
. (11)
Therefore, we see that in the CQ case, RSDs do not allow us to recon-
structthelarge-scalegravitationalpotentialΨLS
,eventhoughthefifth
force does not act directly on baryons.
TolinkthistostandardRSDanalyses,werelatethegalaxyvelocity
tothematterdensitycontrast,assumingthatthecontinuityequation
isvalidinbothmodels(Methods).Withthis,theRSDpowerspectrum
becomes
Pgal
(k, μk, z) = (b2
+ μ2
k
f)
2
Pδδ(k, z) , (12)
where f ≡ d ln δ/d ln a is the growth rate and Pδδ is the matter
power spectrum. Both f and Pδδ are determined by the solution to
equation (4) and, therefore, directly affected by Geff that has similar
forms in GBD and CQ (equation (5)).
The second relevant observable is WL, measured through
cosmic shear or lensing of the cosmic microwave background.
The WL convergence, κ, probes the sum of the two gravitational
potentialsvia
κ(n, z) = ∫
r(z)
0
dr′ r(z) − r′
2r(z)r′
∆Ω(Φ + Ψ) (n, r′
) , (13)
where r is the comoving distance to the source and ΔΩ is the Laplace
operator on the sphere. As for RSDs, the correlations of conver-
gence over large distances are affected by only the large-scale part of
the potentials. Lensing correlations, therefore, effectively provide a
measurementofthepowerspectrumofΦLS
+ ΨLS
,whichcanberelated
to Pδδ through equation (7)
P(Φ+Ψ)
(k, z) = 9H4
0
Ω2
m(1 + z)
2
Σ2
(k, z)Pδδ(k, z) , (14)
whereH0 istheHubblefactortodayandΩm isthematterdensityparam-
eter.WLmeasurementsarethereforesensitivetotwoingredients:the
parameter Σ, which links the gravitational potentials to the density
fluctuation,andtheeffectivegravitationalcouplingGeff,whichaffects
the density power spectrum Pδδ.
From equations (12) and (14), we see that combining WL with
RSDallowsonetomeasurebothGeff andΣsimultaneously.Fromthose,
we can infer μfit
and ηfit
that one would obtain under the assumption
thatEulerequationisunmodified.ForGBD,wehave
μfit
=
GGBD
eff
G
= μGBD
> 1 , (15)
ηfit
=
2Σfit
μfit
− 1 =
2
μfit
− 1 = ηGBD
< 1 , (16)
that is, we would observe a non-zero gravitational slip, ηfit
< 1, as
expected. For CQ, we have
μfit
=
GCQ
eff
G
> 1 (17)
Galaxy
Large-scale
structure
ψLS
ψloc
Fig.1|Thelarge-scaleandthelocalΨ.Illustrationofthelarge-scaleandlocal
contributionofthegravitationalpotentialΨ.
2
RSD
Lensing
1
0
0 1 2
Σ
fit
= µ(1 + η)
1
2
µ
fit
=
G
eff
G
Fig.2|RSDandWLconstraintsonμandΣ.Illustrationoftheconstraintsonμ
andΣfromcombinedmeasurementsofRSDandWL.Theobservedμfit
isrelated
toGeff,henceaffectedbyadarkfifthforce.TheobservedΣfit
,incontrast,isrelated
tothetrueμ,thatis,theonethatentersintoPoissonequationandthatisexactly
equaltooneinmodelswithadarkforce.
4. Nature Astronomy
Analysis https://doi.org/10.1038/s41550-023-02003-y
ηfit
=
2Σfit
μfit
− 1 =
2
μfit
− 1 < 1 . (18)
Hence,eventhoughthegravitationalslipiszeroinCQ,onewouldstill
measureηfit
< 1bycombiningRSDwithWL.Thisclearlydemonstrates
thatmeasuringη ≠ 1fromRSDandWLisnotasmokinggunformodified
gravity—it can also be due to a fifth force acting solely on DM.
While we used CQ as our example, the effective gravitational slip
is present in any model that breaks the weak equivalence principle
for DM, that is, any model where a dark force is acting solely on DM.
As is schematically shown in Fig. 2, RSDs provide constraints on μfit
(green region), whereas WL constrains both μfit
and Σfit
(blue region).
As lensing probes the geometry of the Universe, Σfit
is always equal to
the true Σ entering in equation (14). Therefore, even if there is a dark
fifthforce,Σfit
isrelatedtothetrueηandμ.Incontrast,μfit
isfittedusing
theevolutionequationforthedensitycontrast,whichdependsonGeff.
Therefore, if there is a dark fifth force, μfit
differs from the true μ. As a
consequence,whencombiningΣfit
= μ(1 + η)/2 = 1withμfit
> 1inmodels
withadarkforce,weautomaticallyobtainηfit
< 1.
In ref. 19, it was argued that this problem could be circumvented
by using RSDs to measure directly the Newtonian potential Ψ,
instead of constraining Geff (and hence μfit
) through the growth rate.
However, as the RSD power spectrum is governed by the galaxy
centre of mass, θg, which is affected by the effective gravitational
potential Ψeff
(equation (11)), this method would also lead to a
measurementofηfit
< 1(seeMethodsforadetailedderivation).
Distinguishingmodifiedgravityfromadarkforce
withgravitationalredshift
Fortunately, the coming generation of galaxy surveys will allow us
to measure a new observable, gravitational redshift, which can be
used to unambiguously distinguish between a dark fifth force and
a modification of gravity.
Asexplainedabove,themainproblemwithmeasuringηfromRSDs
andWListhatRSDsarenotatracerofthetruelarge-scalegravitational
potential, ΨLS
, if DM is affected by a fifth force. However, there are
otherdistortionscontributingtotheobservedgalaxynumbercounts
Δ(refs.25–27).Amongtheseeffects,oneisparticularlyimportantfor
testinggravity:theeffectofgravitationalredshift.Thiseffectencodes
thefactthatwhenlightescapesagravitationalpotential,itsenergyis
redshifted. Contrary to WL, which is sensitive to the sum of the two
gravitational potentials (both time and space distortions deviate the
trajectoryoflight),theshiftinenergyisduetoonlythetimedistortion.
Therefore,gravitationalredshiftprovidesameasurementofthetrueΨ,
eveninthepresenceofafifthforce.CombiningthiswithWLwillallow
ustomeasurethetruegravitationalslipand,consequently,distinguish
adarkfifthforcefromamodificationofgravity.
In practice, the gravitational redshift contribution to Δ is very
small, and contributes in a negligible way to standard analyses. How-
ever, this effect has the specificity to generate asymmetries in the
distributionofgalaxies28
.Forthisreason,itwasproposedtoisolateit
by searching for asymmetries in the cross-correlation of two popula-
tionsofgalaxies,forexampleabright(B)andfaint(F)population28–30
.
Gravitationalredshiftis,however,nottheonlycontributionthatgener-
ates asymmetries in the correlation function: there are also Doppler
effects, proportional to the galaxy centre-of-mass velocity, that have
thesameproperty28,31
.Anymeasuredasymmetrywill,therefore,bedue
to a combination of these Doppler terms and gravitational redshift.
These terms are generally called relativistic effects in the literature,
even though, in reality, only gravitational redshift is a pure effect of
generalrelativity.Theycontributetothegalaxynumbercountsas:
∆rel
(k, z)
= iμk [−
k
ℋ
Ψ(k, z) + (1 − 5s +
5s−2
ℋr
−
̇
ℋ
ℋ2
+ fevol
)
θg(k,z)
k
+
̇
θg(k,z)
kℋ
] ,
where s is the magnification bias and fevol
is the evolution bias.
Contrary to RSDs, these relativistic effects generate contributions
to the galaxy power spectrum with odd powers of μk, and can be
isolated by looking for a dipole and octupole. The dipole, which is
the dominant contribution, is given by
P
(1)
BF
(k, z) = i α (f, ̇
f, ΘB, ΘF)
ℋ
k
Pδδ(k, z) + i(bB − bF)
k
ℋ
PδΨLS (k, z) ,
(19)
whereαisagenericfunctionofthegrowthratefanditstimederivative
as well as of ΘB and ΘF that encode the dependence of the dipole on
the bias, magnification bias and evolution bias of the bright and
faint population, respectively. The dipole is suppressed by one
power of ℋ/k with respect to the even multipoles (Methods), and
itisconsequentlytoosmalltobemeasuredincurrentsurveys32
.How-
ever, forecasts have shown that it will be detectable with high signifi-
cancewiththecominggenerationofsurveys,suchastheDarkEnergy
Spectroscopic Instrument (DESI) and the Square Kilometer Array
(SKA2)33,34
.
Fromequation(19),weseethatcombiningthedipolewiththeeven
multipoles (that depend on Pδδ) allows one to directly measure
PδΨLS (k, z) (refs. 35,36), which can be used to unambiguously distin-
guish between modified gravity and a dark fifth force. In practice,
this can be done in two complementary ways. The first possibility is
to look directly for modifications of gravity by combining PδΨLS (k, z)
withgalaxy–galaxylensing(see,forexample,ref.37),whichmeasures
the correlation of density with lensing: Pδ(ΦLS+ΨLS)(k, z). The ratio of
thesetwomeasuredquantitiesgivesη:
Pδ(ΦLS+ΨLS)(k,z)
PδΨLS (k,z)
= 1 + η(k, z) . (20)
In ref. 38 it was shown that, with this method, η can be measured
with a precision of 20–30% at low redshift (in 4 bins, between z = 0.2
and z = 0.7), by combining spectroscopic measurements from SKA2
and photometric measurements from the Vera Rubin Observa-
tory39
. Since the denominator of equation (20) depends on the true
gravitational potential, a detection of η ≠ 1 with this method would
truly be a smoking gun for modified gravity. Models with a dark fifth
force would give η = 1.
The second way of using PδΨLS (k, z) to distinguish between
modified gravity and a dark fifth force is to combine it with RSDs to
directly test the validity of the weak equivalence principle, that is, to
constrain the strength of the fifth force34
. More precisely, one can
compare PδΨLS (k, z)with Pδθg
(k, z)measuredfromRSD,todirectlyprobe
Eulerequationforgalaxiesinequations(10)and(11),andmeasurethe
fifth force, proportional to β in the case of CQ. In ref. 21, it was shown
that, with this method, modifications of Euler equation can be con-
strainedanddisentangledfromachangeinthePoissonequationatthe
level of 15%, with SKA2. Note that these forecasts were based on a
particularparameterizationinwhichmodificationswereproportional
to the dark energy density fraction, as commonly assumed in other
literature40
. The constraints would be tighter in models where devia-
tionscouldoccuratearlierepochs.
Conclusions
Current data are not able to distinguish unambiguously between
modifications to Einstein equations and modifications to Euler
equation. The limitation is due to the fact that large-scale structure
is described by four fields, δg, θg, Φ and Ψ, whereas current observa-
tions can measure only three quantities, δg, θg and Φ + Ψ. Measuring
thegalaxydipolewithfuturesurveyswilladdthemissinginformation,
allowingonetodifferentiatebetweenadarkfifthforceandamodifica-
tion of gravity.
5. Nature Astronomy
Analysis https://doi.org/10.1038/s41550-023-02003-y
Methods
Effective gravitational couplings in GBD and CQ
To derive equations (4) and (5), for simplicity, we will adopt the
quasi-staticapproximation,inwhichonerestrictstosubhorizonscales
andassumesthatthetimederivativesofthemetricandthescalar-field
perturbations are much smaller than their spatial derivatives. Under
thequasi-staticapproximation,inFourierspace,therelevantequations
inthebaryonframeareasfollows.
GeneralizedBrans–Dicke(GBD):
k2
Φ = −4πGa2
(ρbδb + ρcδc) − βk2
δϕ (21)
k2
(Φ − Ψ) = −2βk2
δϕ (22)
̇
δb + θb = 0 (23)
̇
θb + ℋθb = k2
Ψ (24)
̇
δc + θc = 0 (25)
̇
θc + ℋθc = k2
Ψ (26)
δϕ = −
β( ρcδc + ρbδb)
m2 + k2/a2
(27)
ϕ = V,ϕ + β(ρc + ρb) ≡ Veff
,ϕ (28)
̈
δ + ℋ ̇
δ = 4πGa2
ρδ [1 +
2 ̃
β2
k2
a2m2 + k2
] (29)
Coupledquintessence(CQ):
k2
Φ = −4πGa2
(ρbδb + ρcδc) (30)
k2
(Φ − Ψ) = 0 (31)
̇
δb + θb = 0 (32)
̇
θb + ℋθb = k2
Ψ (33)
̇
δc + θc = 0 (34)
̇
θc + (ℋ + β ̇
ϕ)θc = k2
Ψ + k2
βδϕ (35)
δϕ = −
βρcδc
m2 + k2/a2
(36)
ϕ = V,ϕ + βρc ≡ Veff
,ϕ (37)
̈
δ + ℋ ̇
δ = 4πGa2
ρδ [1 +
2 ̃
β2
k2
a2m2 + k2
(
ρc
ρ
)
2
(
δc
δ
)] (38)
where the overdots denote derivatives with respect to the conformal
time τ, □=∇μ∇μ
, ℋ = a−1
da/dτ , β = A,ϕ/A is the scalar-field coupling
strength, ̃
β2
= β2
/8πG and m2
= Veff
,ϕϕ
, with the effective potentials
defined via equations (28) and (37). Note that the effective potential
in CQ depends on only DM. For simplicity, we assume here that A−2
≈ 1
and neglect it in our equations. In the case of GBD, this implies that
our G is the G today, while the overall change in the gravitational
coupling with redshift is constrained to be very small in screened
GBD theories41
. In the case of CQ, an A2
≠ 1 would simply re-scale β
inourequations.
We see that the Euler equation for DM in CQ (equation (35)) con-
tains a friction term β ̇
ϕθc. This term can be important in CQ models
in which ̇
ϕ ≈ ℋ (ref. 42). It is, however, negligible in theories such
as the chameleon43
or the symmetron44
models, in which the scalar
field remains near the minimum of a slowly changing effective
potential.Inwhatfollows,weignorethistermforsimplicity,as,forour
purposes,itissufficienttofindoneexamplewhereonecannotdistin-
guish GBD from CQ. Either way, the presence of this term would not
affectourarguments,asanymodificationoftheEulerequationwould
yield an effective potential that is different from the true Ψ if the RSD
measurements are interpreted assuming an unmodified Euler
equation.
One can see that in GBD theories, there is an extra term in the
Poissonequation(21),andinadditionthetwopotentialsaredifferent
(equation(22)),Φ ≠ Ψ,henceη ≡ Φ/Ψ ≠ 1.Onecancombineequations
(21), (22) and (27) to write separate Poisson equations for the poten-
tial Ψ, which affects the motion of non-relativistic matter (through
equations(24)and(26)),andtheWeylpotentialΦ + Ψfeltbyrelativistic
particles:
k2
Ψ = −4πGa2
[1 +
2 ̃
β2
k2
a2m2 + k2
] (ρbδb + ρcδc) , (39)
k2
(Φ + Ψ) = −8πGa2
(ρbδb + ρcδc) . (40)
Comparingtheabovetothecommonlyusedphenomenologicalparam-
eterizationofmodifiedgravityeffectsoncosmologicalperturbations
k2
Ψ = −4πμ(a, k)Ga2
(ρbδb + ρcδc) (41)
k2
(Φ + Ψ) = −8πΣ(a, k)Ga2
(ρbδb + ρcδc) , (42)
wehave
μ = 1 +
2 ̃
β2
k2
a2m2 + k2
, Σ =
1
2
μ(1 + η) = 1 . (43)
Thus,GBDtheoriespredictμ ≠ Σ.Notethatthisistrueevenifwedonot
assume A−2
≈ 1, in which case μ = A2
(1 + 2 ̃
β2
k2
/(a2
m2
+ k2
)) and Σ = A2
.
Moreover,wecancombinethecontinuityandEulerequations,anduse
equation(27),toderiveasecond-orderequationdescribingtheevolu-
tionofthetotalmatterdensitycontrastδ = (ρbδb + ρcδc)/(ρb + ρc),given
by equation (29), which can be interpreted as growth in the presence
ofaneffectivegravitationalcoupling, GGBD
eff
,definedas
GGBD
eff
G
= μ = 1 +
2 ̃
β2
k2
a2m2 + k2
. (44)
Incontrast,inthecaseofCQ,theEinsteinequationsarenotmodi-
fiedand,formally,μ = Σ = η = 1.Theeffectofthescalarforceonstructure
growth comes through the new term in the Euler equation for DM
(equation(35)).Thesecond-orderequationforthetotalmatterdensity
contrast, δ, in this case, is given by equation (38), which can also be
interpreted as growth in the presence of an effective gravitational
coupling, GCQ
eff
,definedas
GCQ
eff
G
= 1 +
2 ̃
β2
k2
a2m2 + k2
(
ρc
ρ
)
2
(
δc
δ
) . (45)
6. Nature Astronomy
Analysis https://doi.org/10.1038/s41550-023-02003-y
We see that GCQ
eff
/G and GGBD
eff
/G are very similar to each other. The only
difference is a small suppression of the impact of the fifth force in
GCQ
eff
,duetothefactthat~15%ofmatterdoesnotfeelthefifthforce.
Gravitationalslipmeasuredfromgalaxypeculiarvelocities
andweaklensing
ThefactthatΦ ≠ ΨinGBD,whileΦ = ΨinCQ,suggeststhatonecould
differentiate the two cases by measuring η (refs. 13,19), making it a
smoking gun for modified gravity. Note that there exist scalar-tensor
theories with no gravitational slip, such as cubic Galileons45
, kinetic
gravitybraiding46
andthe‘no-slipgravity’47
,butthesecanbeviewedas
rareexceptionswithinthebroadclassofHorndeskitheories5,6
.Tomeas-
ure η, one can, in principle, combine weak lensing data, that measure
Φ + Ψandare,consequently,sensitivetoΣ,withameasurementofthe
baryonvelocities,thataredrivenbyΨandare,consequently,sensitive
to μ. The problem with this method is that, in CQ, the baryons too are
affectedbythefifthforceonDMbecausetheyareconfinedingalaxies.
Therefore, baryon velocities are not a true tracer of the gravitational
potential Ψ in this case, and using them would lead to a measured
ηfit
≠ 1evenifthereisnointrinsicgravitationalslip.
To see this, let us start by writing the observed fluctuation in the
galaxynumbercountsas
∆(n, z) = δg −
1
ℋ
∂r(Vb ⋅ n) , (46)
whereristhecomovingdistancetothegalaxiesandnisthedirection
ofobservation.Equation(46)canbeFouriertransformed
∆(k, z) = b δ(k, z) −
1
ℋ
μ2
k
θb(k, z) , (47)
where μk = ̂
k ⋅ nisthecosineoftheanglebetweenthevectorkandthe
direction of observation n (which is considered fixed in the flat-sky
approximation), and b is the bias. The power spectrum of Δ is then
givenby
Pgal
(k, μk, z) = b2
Pδδ(k, z) −
2b
ℋ
μ2
k
Pδθb
(k, z) +
1
ℋ2
μ4
k
Pθbθb
(k, z) . (48)
Since we are interested in the galaxy power spectrum on large scales,
in the linear regime k kNL, we need to model the correlations of the
baryon velocity at those scales. For this, we split the baryon velocity
intotwoparts:thevelocityofthebaryonswithrespecttothecentreof
mass of the galaxy, that we call θloc
b
, and the velocity of the centre of
massofthegalaxywithrespecttotheHubbleflow,thatwecallθg:
θb = θloc
b
+ θg . (49)
In both GBD and CQ models, the velocity of the baryons with respect
tothecentreofmassobeys
̇
θ
loc
b + ℋθloc
b
= k2
Ψ + Fint , (50)
whereFint accountsforthenon-gravitationalinteractionsaffectingthe
motionofbaryonsinsidethegalaxy.Thegravitationalpotentialcanbe
decomposed into a local part, due to the presence of the galaxy, and
a large-scale part, due to the large-scale structure of the Universe, as
showninFig.1
Ψ = Ψloc
+ ΨLS
. (51)
Equation (50) depends on the total gravitational potential Ψ. How-
ever, as the galaxy is a localized object of size that is small compared
withtheextentofΨLS
,thecentreofmassofthegalaxyandthebaryons
are situated at almost the same value of ΨLS
. Consequently, ΨLS
does
not impact the motion of baryons inside the galaxy, that is, with
respect to the centre of mass. In contrast, Ψloc
varies significantly
over the extent of the galaxy and does contribute to equation (50).
Wethereforeobtain
̇
θ
loc
b + ℋθloc
b
= k2
Ψloc
+ Fint . (52)
From this equation, we see that the local velocity is uncorrelated
on scales larger than the size of the galaxy. The internal forces in two
differentgalaxiesareindeeduncorrelated,andthelocalgravitational
potentialsarealsouncorrelatedatlargedistance.Therefore
Pθloc
b
θloc
b
(k, z) = 0, for k ≲ 1/sgalaxy , (53)
wheresgalaxy denotesthetypicalsizeofagalaxy.Asaconsequence,the
RSD power spectrum is affected by only the motion of the centre of
massofthegalaxy
Pgal
(k, μk, z) = b2
Pδδ(k, z) −
2b
ℋ
μ2
k
Pδθg
(k, z) +
1
ℋ2
μ4
k
Pθgθg
(k, z) . (54)
The power spectrum can be further simplified by using that in
both GBD and CQ, baryons and DM obey the continuity equation,
leadingto
θg = − ̇
δ = −ℋfδ , (55)
wherethe(total)mattergrowthrateisdefinedas
f ≡
d ln δ
d ln a
. (56)
Inserting this into equation (54), we obtain equation (12). From this
equation,weseethattheRSDpowerspectrumcanbeusedtomeasure
thegrowthratefandconstrainGeff.Alternatively,itcanalsobeusedto
probe ΨLS
. In GBD, the galaxy centre of mass, θg, obeys equation (10)
and can therefore directly be used to reconstruct ΨLS
. In CQ however,
θg obeys equation (11), meaning that RSD provide a measurement of
Ψeff
ΨLS
due to the fifth force. Comparing Ψeff
with ΦLS
+ ΨLS
inferred
fromlensingwouldgive
ΦLS
+ ΨLS
Ψeff
ΦLS
+ ΨLS
ΨLS
= 2 , leading to ηfit
=
ΦLS
+ ΨLS
Ψeff
− 1 1 , (57)
that is, a detection of non-vanishing gravitational slip. Again, while
we used CQ to illustrate the point, the argument holds for a general
darkforce.
Galaxydistributionmultipoles
In addition to RSDs, the observed fluctuation in the galaxy number
countsisaffectedbyseveralotherdistortions25–27
:
∆rel
(n, z) =
1
ℋ
∂rΨ +
1
ℋ
̇
V ⋅ n + (1 − 5s +
5s − 2
ℋr
−
̇
ℋ
ℋ2
+ fevol
) V ⋅ n , (58)
wherethefirsttermontheright-handsideisthegravitationalredshift
thatprobethetrueNewtonianpotentialΨ.Notethatotherrelativistic
effects contribute to Δ, such as Shapiro time delay, integrated
Sachs–Wolfe and gravitational lensing25–27
. However, these effects
are negligible at the scales and redshifts relevant for the analyses we
describehere48
.
Toseparatetherelativisticeffectsfromthestandarddensityand
RSD,onecanexpandthepowerspectruminmultipolesofμk
P
gal
BF
(k, μk, z) = ∑
ℓ
P
(ℓ)
BF
(k, z)ℒℓ(μk) , (59)
7. Nature Astronomy
Analysis https://doi.org/10.1038/s41550-023-02003-y
where ℒℓ(μk) denotes the Legendre polynomial of order ℓ. Using
thecontinuityequation(55),themultipolescanbewrittenas
Monopole: P
(0)
BF
(k, z) = [bBbF +
1
3
(bB + bF)fm +
1
5
f2
m] Pδδ(k, z) , (60)
Quadrupole: P
(2)
BF
(k, z) = [
2
3
(bB + bF)fm +
4
7
f2
m] Pδδ(k, z) , (61)
Hexadecapole: P
(4)
BF
(k, z) =
8
35
f2
mPδδ(k, z) , (62)
Dipole: P
(1)
BF
(k, z) = iα (fm, ̇
fm, ΘB, ΘF)
ℋ
k
Pδδ(k, z) + i(bB − bF)
k
ℋ
PδΨ (k, z) ,
(63)
Octupole: P
(3)
BF
(k, z) = iβ (fm, ΘB, ΘF)
ℋ
k
Pδδ(k, z) , (64)
whereΘB andΘF encodethedependenceofthemultipolesonthebias,
magnification bias and evolution bias of the bright and faint popula-
tion, respectively. These multipoles can be measured separately by
weighting the galaxy power spectrum with the appropriate Legendre
polynomial
P
(ℓ)
BF
(k, z) =
2ℓ + 1
2
∫
1
−1
dμkℒℓ(μk)P
gal
BF
(k, μk, z) . (65)
Themonopole,quadrupoleandhexadecapoleareroutinelymeas-
uredforonepopulationofgalaxies,see,forexample.ref.49,andalso
for multiple populations50,51
. Measuring these multipoles is actually
the optimal way to extract information from RSD and to infer the
growth rate f. Measuring the dipole is significantly more difficult, as
itssignal-to-noiseratioismuchsmallerthanthatoftheevenmultipoles.
This is due to the fact that the dipole is suppressed by a factor ℋ/k
with respect to the even multipoles. Note that here we show
the multipoles of the power spectrum. In practice, when including
relativistic effects, it is better to work with the multipoles of the
correlation function, as wide-angle corrections can be correctly
accountedforinthiscase.
Dataavailability
Datasharingisnotapplicabletothisarticleasnodatasetsweregener-
atedoranalysedduringthecurrentstudy.
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