On the gravitational wave sources from the NANOGrav 12.5-yr data

TL;DR

This paper analyzes the NANOGrav 12.5-year pulsar timing data to identify potential sources of the observed stochastic gravitational wave background, favoring cosmic strings as the most likely origin.

Contribution

It evaluates multiple early Universe gravitational wave sources using Bayesian analysis, highlighting cosmic strings as the most probable explanation for the observed signal.

Findings

Cosmic strings are the most favored source based on Bayes factor.

Constraints on supermassive black hole mergers are discussed.

Implications for early Universe physics are explored.

Abstract

The NANOGrav Collaboration recently reported a strong evidence for a stochastic common-spectrum process in the pulsar-timing data. We evaluate the evidence of interpreting this process as mergers of super massive black hole binaries and/or various stochastic gravitational wave background sources in the early Universe, including first-order phase transitions, cosmic strings, domain walls, and large amplitude curvature perturbations. We discuss the implications of the constraints on these possible sources. It is found that the cosmic string is the most favored source against other gravitational wave sources based on the Bayes factor analysis.