Constraining cosmological phase transitions with the Parkes Pulsar Timing Array

TL;DR

This paper uses the Parkes Pulsar Timing Array data to search for gravitational waves from early universe phase transitions, setting constraints on models especially at low temperatures around 1-100 MeV.

Contribution

It provides the first constraints on MeV-scale cosmological phase transitions using pulsar timing data, highlighting sensitivity to dark and QCD transitions.

Findings

No detection of stochastic gravitational wave background.

Constraints on phase transition parameters at MeV temperatures.

Pulsar timing is sensitive to low-temperature phase transitions.

Abstract

A cosmological first-order phase transition is expected to produce a stochastic gravitational wave background. If the phase transition temperature is on the MeV scale, the power spectrum of the induced stochastic gravitational waves peaks around nanohertz frequencies, and can thus be probed with high-precision pulsar timing observations. We search for such a stochastic gravitational wave background with the latest data set of the Parkes Pulsar Timing Array. We find no evidence for a Hellings-Downs spatial correlation as expected for a stochastic gravitational wave background. Therefore, we present constraints on first-order phase transition model parameters. Our analysis shows that pulsar timing is particularly sensitive to the low-temperature ($T \sim 1 - 100$ MeV) phase transition with a duration $(\beta/H_*)^{-1}\sim 10^{-2}-10^{-1}$ and therefore can be used to constrain the dark and QCD phase transitions.