Conversion of squeezed gravitons into photons during inflation

TL;DR

This paper investigates the potential conversion of squeezed relic gravitons into photons during inflation, analyzing the effects of magnetic fields and demonstrating the robustness of gravitons against decoherence with a conversion rate of a few percent.

Contribution

It provides a detailed analysis of graviton-photon conversion during inflation considering magnetic fields, introducing a perturbative solution and numerical/analytical squeezing parameters.

Findings

Gravitons are robust against decoherence from magnetic fields.

Conversion rate of gravitons into photons is at most a few percent.

Squeezing parameters are obtained both numerically and analytically.

Abstract

It is believed that relic gravitons are squeezed during inflation. If so, quantum noise induced by them can be significantly enhanced in current interferometers. However, decoherence of the gravitons during cosmic history may change the degree of squeezing. As a first step for analyzing the decoherence of the gravitons, we assume the presence of a sizable magnetic field at the beginning of inflation and study conversion processes of the squeezed gravitons into photons during inflation in the case of minimal coupling between gravitons and photons. We solve the dynamical evolution of a coupled system of gravitons and photons perturbatively and obtain squeezing parameters for the system numerically and analytically. It turns out that the gravitons are robust against the decoherence caused by the cosmological magnetic fields. We also find that the conversion rate of gravitons into photons is at a few percent at most.