Intuitive understanding of non-gaussianity in ekpyrotic and cyclic models

Abstract

It has been pointed out by several groups that ekpyrotic and cyclic models generate significant non-gaussianity. In this paper, we present a physically intuitive, semi-analytic estimate of the bispectrum. We show that, in all such models, there is an intrinsic contribution to the non-gaussianity parameter f_{NL} that is determined by the geometric mean of the equation of state w_{ek} during the ekpyrotic phase and w_{c} during the phase that curvature perturbations are generated and whose value is O(100) or more times the intrinsic value predicted by simple slow-roll inflationary models, f_{NL}^{intrinsic} = O(0.1). Other contributions to f_{NL}, which we also estimate, can increase |f_{NL}| but are unlikely to decrease it significantly, making non-gaussianity a useful test of these models. Furthermore, we discuss a predicted correlation between the non-gaussianity and scalar spectral index that sharpens the test.

10 pages, 4 figures. Sign error corrected and results generalized, conclusions unchanged

References in corpus (17)

• Cosmological parameters from combining the Lyman-alpha forest with CMB, galaxy clustering and SN constraints
• New Ekpyrotic Cosmology
• Generating Ekpyrotic Curvature Perturbations Before the Big Bang
• A smooth bouncing cosmology with scale invariant spectrum
• Non-Gaussianities in New Ekpyrotic Cosmology
• Non-Gaussian Density Fluctuations from Entropically Generated Curvature Perturbations in Ekpyrotic Models
• Non-Gaussianities from ekpyrotic collapse with multiple fields
• Nonlinear perturbations of cosmological scalar fields
• Ekpyrotic collapse with multiple fields
• On the Initial Conditions in New Ekpyrotic Cosmology
• Curvature perturbations from ekpyrotic collapse with multiple fields
• Scale-invariance in expanding and contracting universes from two-field models
• Colliding Branes in Heterotic M-theory
• Modulated Perturbations from Instant Preheating after new Ekpyrosis
• Bouncing Negative-Tension Branes
• Effective Actions for Heterotic M-Theory
• Solution of a Braneworld Big Crunch/Big Bang Cosmology

Cited by in corpus (72)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Bouncing Cosmologies: Progress and Problems
• Ekpyrotic and Cyclic Cosmology
• The shape of primordial non-Gaussianity and the CMB bispectrum
• Primordial non-Gaussianity and Bispectrum Measurements in the Cosmic Microwave Background and Large-Scale Structure
• Primordial non-Gaussianity: large-scale structure signature in the perturbative bias model
• Constraining Running Non-Gaussianity
• Rapidly-Varying Speed of Sound, Scale Invariance and Non-Gaussian Signatures
• Signature of Primordial Non-Gaussianity on Matter Power Spectrum
• Evolution of Metric Perturbations in Quintom Bounce model
• Supersymmetric Galileons
• Supersymmetric P(X,phi) and the Ghost Condensate
• Primordial Non-Gaussianity in the Cosmic Microwave Background
• DBI Realizations of the Pseudo-Conformal Universe and Galilean Genesis Scenarios
• Cosmic Bounces and Cyclic Universes
• The Pseudo-Conformal Universe: Scale Invariance from Spontaneous Breaking of Conformal Symmetry
• Ekpyrotic Non-Gaussianity -- A Review
• Planck 2013 results support the cyclic universe
• Non-Gaussianity of quantum fields during inflation
• Implications of Planck2015 for inflationary, ekpyrotic and anamorphic bouncing cosmologies
• Multifield Cosmological Perturbations at Third Order and the Ekpyrotic Trispectrum
• Adiabatic Ekpyrosis: Scale-Invariant Curvature Perturbations from a Single Scalar Field in a Contracting Universe
• Non-linear Realizations of Conformal Symmetry and Effective Field Theory for the Pseudo-Conformal Universe
• A general mechanism for producing scale-invariant perturbations and small non-Gaussianity in ekpyrotic models
• Ekpyrotic Perturbations With Small Non-Gaussian Corrections
• From Satisfying to Violating the Null Energy Condition
• The Big Bounce in Rainbow Universe
• Generating Scale-Invariant Perturbations from Rapidly-Evolving Equation of State
• The Ghost Condensate in N=1 Supergravity
• Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem
• Non-singular Ekpyrotic/Cyclic model in Loop Quantum Cosmology
• Dark Energy and the Return of the Phoenix Universe
• Non-Gaussianity Generated by the Entropic Mechanism in Bouncing Cosmologies Made Simple
• Small-Field and Scale-Free: Inflation and Ekpyrosis at their Extremes
• Ekpyrotic Cosmology with a Zero-Shear S-Brane
• $\alpha$-vacuum and inflationary bispectrum
• On the Quantum-To-Classical Transition for Ekpyrotic Perturbations
• On Non-Gaussianities in Multi-Field Inflation (N fields): Bi- and Tri-spectra beyond Slow-Roll
• The anamorphic universe
• A geometrical approach to nonlinear perturbations in relativistic cosmology
• Non-Gaussianities of Single Field Inflation with Non-minimal Coupling
• Converting entropy to curvature perturbations after a cosmic bounce
• Loop Quantum Cosmology corrections to inflationary models
• Non-Gaussianity, Isocurvature Perturbation, Gravitational Waves and a No-Go Theorem for Isocurvaton
• Scale Invariance via a Phase of Slow Expansion
• Quantum Circuit Complexity of Primordial Perturbations
• Scale dependent non-Gaussianities in the CMB data identified with Minkowski Functionals and Scaling Indices
• DBI Inflation in N=1 Supergravity
• The Non-Minimal Ekpyrotic Trispectrum
• Probing the Early Universe with the CMB Scalar, Vector and Tensor Bispectrum
• Tachyon Mediated Non-Gaussianity
• Diversity in the Phoenix Universe
• δN versus covariant perturbative approach to non-Gaussianity outside the horizon in multifield inflation
• Strong Coupling Problem with Time-Varying Sound Speed
• Scale-dependent non-Gaussianities in the WMAP data as identified by using surrogates and scaling indices
• No-Go theorems for ekpyrosis from ten-dimensional supergravity
• Non-Gaussianity constrains hybrid inflation
• Conflation: a new type of accelerated expansion
• Fingerprints of a Non-Inflationary Universe from Massive Fields
• Effect of intermediate Minkowskian evolution on CMB bispectrum
• Dynamics of Cosmological Perturbations and Reheating in the Anamorphic Universe
• Fully non-linear equivalence of delta N and covariant formalisms
• Tachyon-Dilaton-induced Inflation as an alpha'-resummed String Background
• Negative non-Gaussianity as a salvager for PBHs with PTAs in bounce
• Non-Gaussianity in Island Cosmology
• Cuscuton Bounce Beyond the Linear Regime: Bispectrum and Strong Coupling Constraints
• Big Bounce Baryogenesis
• Entropic mechanisms with generalized scalar fields in the Ekpyrotic universe
• Primordial Non-Gaussianity from LAMOST Surveys
• Notes on the post-bounce background dynamics in bouncing cosmologies
• Unifying turnaround-bounce cosmology in a cyclic universe considering a running vacuum model
• Gravitational Leptogenesis in Bounce Cosmology