Solid Inflation

TL;DR

This paper introduces a novel solid inflation model driven by scalar fields with unique symmetry breaking, resulting in distinctive non-Gaussianities and perturbation features that differ from standard inflationary theories.

Contribution

The paper proposes a new solid inflation model with a different symmetry breaking pattern, leading to unique predictions for non-Gaussianities and perturbation dynamics.

Findings

Large non-Gaussianities with f_NL ~ 1/(pt.c_s^2)

Peaked non-Gaussianity shape in the squeezed limit with anisotropic features

Absence of adiabatic modes during inflation, but their presence after

Abstract

We develop a cosmological model where primordial inflation is driven by a 'solid', defined as a system of three derivatively coupled scalar fields obeying certain symmetries and spontaneously breaking a certain subgroup of these. The symmetry breaking pattern differs drastically from that of standard inflationary models: time translations are unbroken. This prevents our model from fitting into the standard effective field theory description of adiabatic perturbations, with crucial consequences for the dynamics of cosmological perturbations. Most notably, non-gaussianities in the curvature perturbations are unusually large, with f_NL ~ 1/(\epsilon.c_s^2), and have a novel shape: peaked in the squeezed limit, with anisotropic dependence on how the limit is approached. Other unusual features include the absence of adiabatic fluctuation modes during inflation---which does not impair their presence and near scale-invariance after inflation---and a slightly blue tilt for the tensor modes.