Model-independent approach to effective sound speed in multi-field inflation

Abstract

For any physical system satisfying the Einstein's equations, the comoving curvature perturbations satisfy an equation involving the momentum-dependent effective sound speed, valid for any system with a well defined energy-stress tensor, including multi-fields models of inflation. We derive a general model-independent formula for the effective sound speed of comoving adiabatic perturbations, valid for a generic field-space metric, without assuming any approximation to integrate out entropy perturbations, but expressing the momentum-dependent effective sound speed in terms of the components of the total energy-stress tensor. As an application, we study a number of two-field models with a kinetic coupling between the fields, identifying the single curvature mode of the effective theory and showing that momentum-dependent effective sound speed fully accounts for the predictions for the power spectrum of curvature perturbations. Our results show that the momentum-dependent effective sound speed is a convenient scheme for describing all inflationary models that admit a single-field effective theory, including the effects of entropy perturbations present in multi-fields systems.

arXiv comment19 pages, fig. 6

References in corpus (34)

• The Effective Field Theory of Inflation
• Adiabatic and entropy perturbations from inflation
• Features of heavy physics in the CMB power spectrum
• Scalar perturbations during multiple-field slow-roll inflation
• Effective field theory approach to quasi-single field inflation and effects of heavy fields
• Equilateral Non-Gaussianity and New Physics on the Horizon
• The Gelaton Scenario: Equilateral non-Gaussianity from multi-field dynamics
• Curvature and isocurvature perturbations in two-field inflation
• Effective theories of single field inflation when heavy fields matter
• Quasi-Single Field Inflation with Large Mass
• On the importance of heavy fields during inflation
• Heavy fields, reduced speeds of sound and decoupling during inflation
• Strongly Coupled Perturbations in Two-Field Inflationary Models
• Curvature Perturbation Spectrum in Two-field Inflation with a Turning Trajectory
• Hyperinflation
• Effective Field Theory and Decoupling in Multi-field Inflation: An Illustrative Case Study
• Influence of heavy modes on perturbations in multiple field inflation
• Inflating in a Trough: Single-Field Effective Theory from Multiple-Field Curved Valleys
• Primordial fluctuations and non-Gaussianities in sidetracked inflation
• Primordial perturbations from inflation with a hyperbolic field-space
• Effective field theory of weakly coupled inflationary models
• The Effective Field Theory of Inflation Models with Sharp Features
• Low-Energy Effective Field Theory for Chromo-Natural Inflation
• Hyper non-Gaussianities in inflation with strongly non-geodesic motion
• Cumulative effects in inflation with ultra-light entropy modes
• Decoupling Survives Inflation: A Critical Look at Effective Field Theory Violations During Inflation
• Flattened non-Gaussianities from the effective field theory of inflation with imaginary speed of sound
• The Importance of Slow-roll Corrections During Multi-field Inflation
• Multifield inflation beyond $N_{\mathrm{field}}=2$: non-Gaussianities and single-field effective theory
• On Non-Canonical Kinetic Terms and the Tilt of the Power Spectrum
• Effective field theory in time-dependent settings
• The MESS of cosmological perturbations
• Reconstructing the EFT of Inflation from Cosmological Data
• Decoupling limits in multi-sector supergravities

Cited by in corpus (6)

• The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
• Bootstrapping Multi-Field Inflation: non-Gaussianities from light scalars revisited
• Towards hybrid inflation with $n_s=1$ in light of Hubble tension and primordial gravitational waves
• (Super)Universal Attractors and the de Sitter Vacua in String Landscape
• Effective speed of gravitational waves
• Effective speed of cosmological perturbations