A general mechanism for producing scale-invariant perturbations and small non-Gaussianity in ekpyrotic models

Abstract

We explore a new type of entropic mechanism for generating density perturbations in a contracting phase in which there are two scalar fields, but only one has a steep negative potential. This first field dominates the energy density and is the source of the ekpyrotic equation of state. The second field has a negligible potential, but its kinetic energy density is coupled to the first field with a non-linear sigma-model type interaction. We show that for any ekpyrotic equation of state it is possible to choose the potential and the kinetic coupling such that exactly scale-invariant (or nearly scale-invariant) entropy perturbations are produced. The corresponding background solutions are stable, and the bispectrum of the entropy perturbations vanishes as no non-Gaussianity is produced during the ekpyrotic phase. Hence, the only contribution to non-Gaussianity comes from the non-linearity of the conversion process during which entropic perturbations are turned into adiabatic ones, resulting in a local non-Gaussianity parameter $f_{NL}\sim 5$.

arXiv comment8 pages, 1 figure, accepted for publication in PRD

References in corpus (30)

• The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
• A general proof of the conservation of the curvature perturbation
• Gravitational Wave Spectrum Induced by Primordial Scalar Perturbations
• The shape of non-Gaussianities
• The Atacama Cosmology Telescope: Cosmological parameters from three seasons of data
• New Ekpyrotic Cosmology
• Primordial perturbations and non-Gaussianities in DBI and general multi-field inflation
• Generating Ekpyrotic Curvature Perturbations Before the Big Bang
• Adiabatic and Isocurvature Perturbations for Multifield Generalized Einstein Models
• Non-Gaussianities in New Ekpyrotic Cosmology
• Non-Gaussian Density Fluctuations from Entropically Generated Curvature Perturbations in Ekpyrotic Models
• Towards Anisotropy-Free and Non-Singular Bounce Cosmology with Scale-invariant Perturbations
• Non-Gaussianities from ekpyrotic collapse with multiple fields
• Isocurvature perturbations in the Ekpyrotic universe
• Assisted Contraction
• Harrison--Zeldovich spectrum from conformal invariance
• Intuitive understanding of non-gaussianity in ekpyrotic and cyclic models
• The Pseudo-Conformal Universe: Scale Invariance from Spontaneous Breaking of Conformal Symmetry
• Planck 2013 results support the cyclic universe
• Multifield Cosmological Perturbations at Third Order and the Ekpyrotic Trispectrum
• Note on the production of scale-invariant entropy perturbation in the Ekpyrotic universe
• Ekpyrotic Perturbations With Small Non-Gaussian Corrections
• Colliding Branes in Heterotic M-theory
• Nonlinear perturbations of cosmological scalar fields with non-standard kinetic terms
• Non-Gaussianity Generated by the Entropic Mechanism in Bouncing Cosmologies Made Simple
• On the Quantum-To-Classical Transition for Ekpyrotic Perturbations
• Modulated Perturbations from Instant Preheating after new Ekpyrosis
• The Return of the Phoenix Universe
• Diversity in the Phoenix Universe
• Decoherence Problem in Ekpyrotic Phase

Cited by in corpus (39)

• Cosmology and Fundamental Physics with the Euclid Satellite
• Bouncing Cosmologies: Progress and Problems
• Bouncing Cosmology made simple
• Non-Singular Bouncing Cosmology: Consistency of the Effective Description
• Review of the No-Boundary Wave Function
• Implications of Planck2015 for inflationary, ekpyrotic and anamorphic bouncing cosmologies
• NEC violation in mimetic cosmology revisited
• Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem
• Scale-invariant perturbations in ekpyrotic cosmologies without fine-tuning of initial conditions
• Nonsingular Ekpyrotic Cosmology with a Nearly Scale-Invariant Spectrum of Cosmological Perturbations and Gravitational Waves
• Small-Field and Scale-Free: Inflation and Ekpyrosis at their Extremes
• Running of the scalar spectral index in bouncing cosmologies
• Classical Inflationary and Ekpyrotic Universes in the No-Boundary Wavefunction
• Converting entropy to curvature perturbations after a cosmic bounce
• Higher order derivative coupling to gravity and its cosmological implications
• The Cosmological OTOC: Formulating new cosmological micro-canonical correlation functions for random chaotic fluctuations in Out-of-Equilibrium Quantum Statistical Field Theory
• Cosmology at the top of the ${\alpha }^{\prime }$ tower
• Quantum Circuit Complexity of Primordial Perturbations
• The slow expansion with nonminimal derivative coupling and its conformal dual
• Primordial Gravitational Waves Induced by Magnetic Fields in an Ekpyrotic Scenario
• The Non-Minimal Ekpyrotic Trispectrum
• Primordial features from ekpyrotic bounces
• Spectrum of Cuscuton Bounce
• New Ekpyrotic Quantum Cosmology
• No-Go theorems for ekpyrosis from ten-dimensional supergravity
• Nearly scale-invariant curvature modes from entropy perturbations during graceful exit
• Conflation: a new type of accelerated expansion
• Fingerprints of a Non-Inflationary Universe from Massive Fields
• Gravitational-wave background in bouncing models from semi-classical, quantum and string gravity
• Cosmological initial data for numerical relativity
• Distinguishing cosmological models through quantum signatures of primordial perturbations
• Cuscuton Bounce Beyond the Linear Regime: Bispectrum and Strong Coupling Constraints
• Anamorphic Quasiperiodic Universes in Modified and Einstein Gravity with Loop Quantum Gravity Corrections
• Big Bounce Baryogenesis
• Entropic mechanisms with generalized scalar fields in the Ekpyrotic universe
• Homogeneous Transitions during Inflation: a Description in Quantum Cosmology
• Warm Ekpyrosis
• Notes on the post-bounce background dynamics in bouncing cosmologies
• Gravitational Leptogenesis in Bounce Cosmology