Is a Dissipative Regime During Inflation in Agreement with Observations?

TL;DR

This paper investigates how a dissipative regime during inflation, characterized by a friction coupling to a relativistic fluid, affects the spectral index of curvature perturbations and finds that only very small friction is consistent with observations.

Contribution

It demonstrates that a dissipative regime with significant friction during inflation produces spectral indices incompatible with observational data, regardless of the inflationary potential.

Findings

Large friction leads to unacceptably red spectral index

Small friction (Γ ≪ H) aligns with observations

Results are robust across different inflationary potentials

Abstract

We study the spectral index of curvature perturbations for inflationary models where the driving scalar field is coupled to a relativistic fluid through a friction term $\Gamma$. We find that only a very small friction term - $\Gamma \ll H$, with H being the Hubble parameter during inflation - is allowed by observations, otherwise curvature fluctuations are generated with a spectral index $n_s$ unacceptably red. These results are generic with respect to the inflationary potential and known dependence of the friction term on the scalar field and the energy density of the relativistic fluid. We compare our findings with previous investigations.