# Scale invariance via a phase of slow expansion

@article{Joyce2011ScaleIV, title={Scale invariance via a phase of slow expansion}, author={Austin Joyce and Justin Khoury}, journal={Physical Review D}, year={2011}, volume={84}, pages={023508} }

We consider a cosmological scenario in which a scale-invariant spectrum of curvature perturbations is generated by a rapidly-evolving equation of state on a slowly expanding background. This scenario generalizes the "adiabatic ekpyrotic" mechanism proposed recently in arXiv:0910.2230. Whereas the original proposal assumed a slowly contracting background, the present work shows that the mechanism works equally well on an expanding background. This greatly expands the realm of broader…

## 22 Citations

Strong coupling problem with time-varying sound speed

- Physics
- 2011

For a single scalar field with unit sound speed minimally coupled to Einstein gravity, there are exactly three distinct cosmological solutions which produce a scale invariant spectrum of curvature…

The Pseudo-Conformal Universe: Scale Invariance from Spontaneous Breaking of Conformal Symmetry

- Physics
- 2011

We present a novel theory of the very early universe which addresses the traditional horizon and flatness problems of big bang cosmology and predicts a scale invariant spectrum of perturbations.…

The Scale-invariant Power Spectrum of Primordial Curvature Perturbation in CSTB Cosmos

- Physics
- 2013

We investigate the spectrum of cosmological perturbations in a bounce cosmos modeled by a scalar field coupled to the string tachyon field (CSTB cosmos). By explicit computation of its primordial…

The scale invariant power spectrum of the primordial curvature perturbations from the coupled scalar tachyon bounce cosmos

- Physics
- 2014

We investigate the spectrum of cosmological perturbations in a bounce cosmos modeled by a scalar field coupled to the string tachyon field (CSTB cosmos). By explicit computation of its primordial…

DBI realizations of the pseudo-conformal universe and Galilean Genesis scenarios

- Physics, Mathematics
- 2012

The pseudo-conformal universe is an alternative to inflation in which the early universe is described by a conformal field theory on approximately flat space-time. The fields develop time-dependent…

Horizon-preserving dualities and perturbations in non-canonical scalar field cosmologies

- Physics
- 2012

We generalize the cosmological duality between inflation and cyclic contraction under the interchange a↔H to the case of non-canonical scalar field theories with varying speed of sound. The single…

Reconstruction of a Nonminimal Coupling Theory with Scale-invariant Power Spectrum

- Physics
- 2012

A nonminimal coupling single scalar field theory, when transformed from Jordan frame to Einstein frame, can act like a minimal coupling one. Making use of this property, we investigate how a…

The slow expansion with nonminimal derivative coupling and its conformal dual

- Geology, Mathematics
- 2016

A bstractWe show that the primordial gravitational wave with scale-invariant spectrum might emerge from a nearly Minkowski space, in which the gravity is asymptotic-past free. We illustrate it with a…

## References

SHOWING 1-10 OF 176 REFERENCES

Nearly scale invariant spectrum of adiabatic fluctuations may be from a very slowly expanding phase of the universe

- Physics
- 2003

In this paper we construct an expanding phase with phantom matter, in which the scale factor expands very slowly but the Hubble parameter increases gradually, and assume that this expanding phase…

Generation of a scale-invariant spectrum of adiabatic fluctuations in cosmological models with a contracting phase

- Physics
- 2002

In pre-big-bang and in ekpyrotic cosmology, perturbations on cosmological scales today are generated from quantum vacuum fluctuations during a phase when the Universe is contracting (viewed in the…

Generating Scale-Invariant Perturbations from Rapidly-Evolving Equation of State

- Physics
- 2011

Recently, we introduced an ekpyrotic model based on a single, canonical scalar field that generates nearly scale-invariant curvature fluctuations through a purely ''adiabatic mechanism'' in which the…

Scale invariance in expanding and contracting universes from two-field models

- Physics, Mathematics
- 2007

We study cosmological perturbations produced by the most general two-derivative actions involving two scalar fields, coupled to Einstein gravity, with an arbitrary field space metric, that admit…

Scale-invariance and the strong coupling problem

- Physics, Mathematics
- 2011

The effective theory of adiabatic fluctuations around arbitrary Friedmann-Robertson-Walker backgrounds — both expanding and contracting — allows for more than one way to obtain scale-invariant…

A smooth bouncing cosmology with scale invariant spectrum

- Physics
- 2007

We present a bouncing cosmology which evolves from the contracting to the expanding phase in a smooth way, without developing instabilities or pathologies and remaining in the regime of validity of…

On adiabatic perturbations in the ekpyrotic scenario

- Physics
- 2009

In a recent paper arXiv:0910.2230, Khoury and Steinhardt proposed a way to generate adiabatic cosmological perturbations with a nearly flat spectrum in a contracting Universe. To produce these…

Near Scale Invariance with Modified Dispersion Relations

- Physics
- 2006

We describe a novel mechanism for generating a nearly scale invariant spectrum of adiabatic perturbations during a non-inflationary stage. It relies on a modified dispersion relation that contains…

Towards a Cosmological Dual to Inflation

- Physics
- 2011

We derive all single-field cosmologies with unit sound speed that generate scale invariant curvature perturbations on a dynamical attractor background. We identify three distinct phases: slow-roll…

Cosmological perturbations in a big-crunch-big-bang space-time

- Physics
- 2004

A prescription is developed for matching general relativistic perturbations across singularities of the type encountered in the ekpyrotic and cyclic scenarios, i.e., a collision between orbifold…