Gravitational waves and dark radiation from dark phase transition: Connecting NANOGrav pulsar timing data and hubble tension

Yuichiro Nakai,Motoo Suzuki,Fuminobu Takahashi,Masaki Yamada

doi:10.1016/j.physletb.2021.136238

Yuichiro Nakai, Motoo Suzuki + Show 2 more

Open Access

https://doi.org/10.1016/j.physletb.2021.136238

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Abstract

Recent pulsar timing data reported by the NANOGrav collaboration may indicate the existence of a stochastic gravitational wave background around f∼10−8 Hz. We explore a possibility to generate such low-frequency gravitational waves from a dark sector phase transition. Assuming that the dark sector is completely decoupled from the visible sector except via the gravitational interaction, we find that some amount of dark radiation should remain until present. The NANOGrav data implies that the amount of dark radiation is close to the current upper bound, which may help mitigate the so-called Hubble tension. If the existence of dark radiation is not confirmed in the future CMB-S4 experiment, it would imply the existence of new particles feebly interacting with the standard model sector at an energy scale of O(1 - 100) MeV.

Highlights

Introduction.– The direct detection of gravitational waves (GWs) by the LIGO and Virgo collaborations [1] has opened up a fascinating era of astronomy and cosmology that looks at our Universe through entirely new eyes
The NANOGrav collaboration of a pulsar timing array (PTA) experiment has analyzed their 12.5 years of data and reported a signal that may be interpreted as a GW background [10]
We explore an interpretation of the reported NANOGrav signal in terms of a stochastic GW background generated by a new strongly first-order phase transition which occurred in a dark sector

Summary

Introduction

Introduction.– The direct detection of gravitational waves (GWs) by the LIGO and Virgo collaborations [1] has opened up a fascinating era of astronomy and cosmology that looks at our Universe through entirely new eyes. [40] discussed a range of GW frequencies covered by PTAs. In this paper, we focus on the first order phase transition in the dark sector decoupled from the visible sector.

Results

Conclusion