Searching for cosmic string induced stochastic gravitational wave background with the Parkes Pulsar Timing Array

TL;DR

This paper searches for gravitational wave backgrounds from cosmic strings using 15 years of pulsar timing data, setting new constraints on string parameters and highlighting the complementarity with high-frequency detectors.

Contribution

It provides the first constraints on cosmic string models from pulsar timing array data and compares these with high-frequency gravitational wave experiments.

Findings

Constraints on string tension Gμ<10^{-11} to 10^{-10}

More stringent than LIGO-Virgo for one model

Highlights pulsar timing arrays' role in probing early Universe physics

Abstract

We search for stochastic gravitational wave background emitted from cosmic strings using the Parkes Pulsar Timing Array data over 15 years. While we find that the common power-law excess revealed by several pulsar timing array experiments might be accounted for by the gravitational wave background from cosmic strings, the lack of the characteristic Hellings-Downs correlation cannot establish its physical origin yet. The constraints on the cosmic string model parameters are thus derived with conservative assumption that the common power-law excess is due to unknown background. Two representative cosmic string models with different loop distribution functions are considered. We obtain constraints on the dimensionless string tension parameter $G\mu<10^{-11}\sim10^{-10}$, which is more stringent by two orders of magnitude than that obtained by the high-frequency LIGO-Virgo experiment for one model, and less stringent for the other. The results provide the chance to test the Grand unified theories, with the spontaneous symmetry breaking scale of $U(1)$ being two-to-three orders of magnitude below $10^{16}$ GeV. The pulsar timing array experiments are thus quite complementary to the LIGO-Virgo experiment in probing the cosmic strings and the underlying beyond standard model physics in the early Universe.