The SEENET-MTP Workshop BW2011 Particle Physics from TeV to Plank Scale 28 August – 1 September 2011, Donji Milanovac, Serbia

1. Inflation … Or What?
Will Kinney
Seenet­MTP Workshop
Balkan Summer Institute, Donji Milanovac
31 August 2011

2. CMB: Basic Properties
Adiabatic density perturbations
Superhorizon correlations
Gaussian statistics
Near scale­invariance over a factor of
1000 in wavelength
Q: What does this really tell us?

3. Generation of Perturbations
Horizon
Mode freezing

4. Generation of Perturbations
Comoving horizon:
Decelerating Expansion:
Accelerating Expansion:
Key ingredient for generation of perturbations:
shrinking horizon

5. The Comoving Horizon in Inflation
Decelerating
Accelerating

6. The Comoving Horizon in Inflation

7. Mode Exit and Re­entry
re­entry
classical
exit
quantum

8. Larger Scales Exit Earlier

9. Superhorizon Perturbations

10. The Horizon Is Not The Horizon
The Hubble length is not
the causal horizon in inflation.
Mode freezing has absolutely
nothing to do with causality.

11. The Horizon Is Not The Horizon
In general, the Hubble length is not even the freezeout horizon:
Scale invariance and freezeout:

12. Is Inflation the Only Way?
Comoving Horizon
(constant equation of state):
Decelerating Expansion:
Accelerating Expansion:
Duality:
(Boyle, et al., hep­th/0403026)

13. The Comoving Hubble Horizon in Inflation
Decelerating
Accelerating

14. The Comoving Hubble Horizon in Bouncing Cosmology
Expansion
Bounce
Contraction

15. The Cyclic Dual to Slow Roll
Slow Roll

16. The Cyclic Dual to Slow Roll
Slow Roll

17. The Cyclic Dual to Slow Roll
Slow Roll
Dual­Slow Roll
Quasi­static contraction

18. Perturbations
Slow Roll Dual­Slow Roll
(WHK, Moradinezhad Dizgah, arXiv:1007.0753)

19. Ekpyrosis: Problems
Shrinking proper Hubble length:
blue spectra
Instabilities: growing mode
Negative potential
Singular bounce
Name sounds like a skin disease
Buchbinder, Khoury & Ovru, PRD 76, 123503 (2007)
Khoury & Steinhardt, arXiv:0910.2230
Linde, Mukhanov & Vikman, arXiv:0912.0944

20. Generating Superhorizon Perturbations
New result:
In an expanding universe, to generate
perturbations consistent with observation, you
must have one of:
(1) Accelerated Expansion
(2) Superluminal Sound Speed
(3) Super­Planckian Energy Density
(Geshnizjani, WHK, Moradinezhad Dizgah, arXiv:1107.1241)

21. Non­Canonical Lagrangians as Bimetric Theories
Lagrangian with arbitrary kinetic term:
Acoustic metric
Light cone:
Two horizons!
Acoustic cone:

22. Light Cones in DBI Inflation
 Acoustic Cone:
Light cone:
x
y

23. Mode Freezing and Horizons
Tensor modes freeze out at the
Hubble Horizon
Scalar modes freeze out at the
Acoustic Horizon
Curvature perturbations generated
by shrinking acoustic horizon!
(Garriga & Mukhanov, arXiv:hep­th/9904176)

24. Horizons in DBI Inflation
Hubble Horizon
Acoustic Horizon

25. Beyond Inflation
For we still need inflation to generate superhorizon
perturbations.
Tachyacoustic Cosmology
: generate superhorizon perturbations in a
radiation­ or matter­dominated universe
Armendariz­Picon, arXiv:astro­ph/0606168 Piao, arXiv:gr­qc/0609071
Magueijo, arXiv:08030859
Bessada, WHK, Stojkovic, Wang, arXiv:0908.3898
Causally self­consistent cosmology: no timelike loops.
Babichev, Mukhanov & Vikman, arXiv:0708.0561

26. Light Cones in Tachyacoustic Cosmology
 Acoustic Cone:
Light cone:
x
y

27. The Tachyacoustic Solution
Decelerating Expansion:
Decaying Sound Speed:

28. Horizons in Tachyacoustic Cosmology
Hubble Horizon:
Acoustic Horizon:
Hubble Horizon grows
(no tensor modes!)
Acoustic Horizon shrinks

29. Horizons in Tachyacoustic Cosmology
Hubble Horizon
Acoustic Horizon

30. Perturbations in Tachyacoustic Cosmology
Hubble Horizon:
Acoustic Horizon:
(Magueijo, arXiv:0803.0859)
(Bessada, WHK, Stojkovic, Wang, arXiv:0908.3898)

31. Tachyacoustic Cosmology: Problems
String embedding problematic
Does not solve flatness problem
Initial singularity
Is it a dynamical attractor?
(Preliminary: yes)

32. Summary
The Hubble length is not the horizon.
Expanding universe: only three ways to get scale
invariance for a sufficient range of super­Hubble
perturbations:
Accelerated expansion
Superluminal sound speed
Transplanckian energy density
Nothing works nearly as well as inflation.