Anisotropic tensor power spectrum at interferometer scales induced by tensor squeezed non-Gaussianity

TL;DR

This paper proposes an inflationary model with broken symmetries that produces a scale-dependent, anisotropic gravitational wave background with enhanced non-Gaussianity, potentially detectable by interferometers.

Contribution

It introduces a novel inflationary scenario where tensor modes acquire mass and non-Gaussianity is amplified, leading to distinctive anisotropic signatures in the primordial gravitational wave background.

Findings

Primordial tensor modes can evade the Higuchi bound due to interactions.

The model predicts a scale-dependent, anisotropic SGWB detectable at interferometer scales.

Tensor non-Gaussianity is significantly enhanced in the squeezed limit, creating observable quadrupolar anisotropy.

Abstract

We develop a scenario of inflation with spontaneously broken time and space diffeomorphisms, with distinctive features for the primordial tensor modes. Inflationary tensor fluctuations are non adiabatic, and can acquire a mass during the inflationary epoch. They can evade the Higuchi bound around de Sitter space, thanks to interactions with the fields driving expansion. Correspondingly, the primordial stochastic gravitational wave background (SGWB) is characterised by a tuneable scale dependence, and can be detectable at interferometer scales. In this set-up, tensor non-Gaussianity can be parametrically enhanced in the squeezed limit. This induces a coupling between long and short tensor modes, leading to a specific quadrupolar anisotropy in the primordial SGWB spectrum, which can be used to build estimators for tensor non-Gaussianity. We analyse how our inflationary system can be tested with interferometers, also discussing how an interferometer can be sensitive to a primordial anisotropic SGWB.