Breaking of Spatial Diffeomorphism Invariance, Inflation and the Spectrum of Cosmological Perturbations

TL;DR

This paper investigates how breaking spatial diffeomorphism invariance during inflation can produce a blue tensor spectrum alongside a red scalar tilt, potentially aligning with string gas cosmology predictions.

Contribution

It explores conditions under which a blue tensor tilt and red scalar tilt coexist in models breaking spatial diffeomorphism invariance, extending previous theoretical frameworks.

Findings

Blue tensor spectrum achievable without violating Null Energy Condition

Conditions for coexistence of blue tensor and red scalar tilts identified

Potential to reproduce string gas cosmology consistency relations

Abstract

Standard inflationary models yield a characteristic signature of a primordial power spectrum with a red tensor and scalar tilt. Nevertheless, Cannone et al recently suggested that, by breaking the assumption of spatial diffeomorphism invariance in the context of the effective field theory of inflation, a blue tensor spectrum can be achieved without violating the Null Energy Condition. In this context, we explore in which cases a blue tensor tilt can be obtained along with a red tilt in the scalar spectrum. Ultimately, we analyze under which conditions this model can reproduce the specific consistency relation of String Gas Cosmology.