Primordial massive gravitational waves from Einstein-Chern-Simons-Weyl gravity

TL;DR

This paper studies the behavior of primordial massive gravitational waves during de Sitter inflation within Einstein-Chern-Simons-Weyl gravity, revealing how different modes decay or vanish depending on mass and conformal invariance.

Contribution

It demonstrates the evolution and decay of vector and tensor modes in Einstein-Chern-Simons-Weyl gravity, highlighting the effects of mass and conformal invariance on primordial gravitational waves.

Findings

Vector power spectrum decays rapidly in superhorizon limit

Massive tensor modes' power spectrum also decays quickly

Vector and tensor spectra vanish when $m^2 o 0$, indicating decoupling from the background

Abstract

We investigate the evolution of cosmological perturbations during de Sitter inflation in the Einstein-Chern-Simons-Weyl gravity. Primordial massive gravitational waves are composed of one scalar, two vector and four tensor circularly polarized modes. We show that the vector power spectrum decays quickly like a transversely massive vector in the superhorizon limit $z\to 0$. In this limit, the power spectrum coming from massive tensor modes decays quickly, leading to the conventional tensor power spectrum. Also, we find that in the limit of $m^2 \to 0$ (keeping the Weyl-squared term only), the vector and tensor power spectra disappear. It implies that their power spectra are not gravitationally produced because they (vector and tensor) are decoupled from the expanding de Sitter background, as a result of conformal invariance.