Search for the Gravitational-wave Background from Cosmic Strings with the Parkes Pulsar Timing Array Second Data Release

TL;DR

This study searches for a gravitational-wave background from cosmic strings using pulsar timing data, setting new upper limits on string tension and constraining models inspired by string theory.

Contribution

It provides the first direct search for an isotropic SGWB from cosmic strings with PTA data and tightens existing bounds on cosmic string tension.

Findings

No evidence for the SGWB from cosmic strings was found.

Upper limit on cosmic string tension is Gμ ≲ 5.1 × 10⁻¹⁰ for p=1.

Constraints are significantly tighter than previous burst-based bounds.

Abstract

We perform a direct search for an isotropic stochastic gravitational-wave background (SGWB) produced by cosmic strings in the Parkes Pulsar Timing Array second data release. We find no evidence for such an SGWB, and therefore place $95\%$ confidence level upper limits on the cosmic string tension, $G\mu$, as a function of the reconnection probability, $p$, which can be less than 1 in the string-theory-inspired models. The upper bound on the cosmic string tension is $G\mu \lesssim 5.1 \times 10^{-10}$ for $p = 1$, which is about five orders of magnitude tighter than the bound derived from the null search of individual gravitational wave burst from cosmic string cusps in the PPTA DR2.