W. Kinney - Scale-Invariant Perturbations: is Inflation the only Way?

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

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?

Generation of Perturbations Horizon Mode freezing

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

The Comoving Horizon in Inflation Decelerating Accelerating

The Comoving Horizon in Inflation

Mode Exit and Reentry reentry classical exit quantum

Larger Scales Exit Earlier

Superhorizon Perturbations

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.

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

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

The Comoving Hubble Horizon in Inflation Decelerating Accelerating

The Comoving Hubble Horizon in Bouncing Cosmology Expansion Bounce Contraction

The Cyclic Dual to Slow Roll Slow Roll

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

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

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

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)

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

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

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)

Horizons in DBI Inflation Hubble Horizon Acoustic Horizon

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

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

The Tachyacoustic Solution Decelerating Expansion: Decaying Sound Speed:

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

Horizons in Tachyacoustic Cosmology Hubble Horizon Acoustic Horizon

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

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

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.

W. Kinney - Scale-Invariant Perturbations: is Inflation the only Way?

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W. Kinney - Scale-Invariant Perturbations: is Inflation the only Way? Presentation Transcript