A peak in the power spectrum of primordial gravitational waves induced by primordial dark magnetic fields

TL;DR

This paper investigates how primordial dark magnetic fields during inflation can induce a peak in the power spectrum of primordial gravitational waves, offering a new way to probe dark magnetic fields through gravitational wave observations.

Contribution

It introduces the concept that primordial dark magnetic fields cause a peak in PGWs' power spectrum via graviton-dark photon conversion, highlighting a novel observational signature.

Findings

Primordial dark magnetic fields induce a peak in PGWs' spectrum.

The peak's height varies with observation direction.

Peak frequency range is from 10^{-5} to 10^{3} Hz for GUT scale inflation.

Abstract

Dark gauge fields have been discussed as candidates for dark matter recently. If they existed, primordial dark magnetic fields during inflation would have existed. It is believed that primordial gravitational waves (PGWs) arise out of quantum fluctuations during inflation. We study the graviton-dark photon conversion process in the presence of background primordial dark magnetic fields and find that the process induces the tachyonic instability of the PGWs. As a consequence, a peak appears in the power spectrum of PGWs. It turns out that the peak height depends on the direction of observation. The peak frequency could be in the range from $10^{-5}$ to $10^{3}$ Hertz for GUT scale inflation. Hence, the observation of PGWs could provide a new window for probing primordial dark magnetic fields.