Gravitational Waves and Dark Radiation from Dark Phase Transition: Connecting NANOGrav Pulsar Timing Data and Hubble Tension

by Dr Motoo Suzuki (TDLI)

Monday 7 Jun 2021, 10:30 → 12:00 Asia/Shanghai

Tsung-Dao Lee library/Fourth Floor-410 - 410# Meeting Room (Tsung-Dao Lee Library)

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. I also talk about a recent paper from NANOGrav collaboration about the phase transition.

Tencent information:

https://meeting.tencent.com/s/GYPDwkN6U7wt

ID: 255 764 695

password: 848002