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?
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)
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)
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)
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.