Imprints of relic gravitational waves on pulsar timing

TL;DR

This paper investigates how relic gravitational waves from inflation could imprint on pulsar timing residuals, providing a method to detect them and setting new constraints based on recent observations and cosmological data.

Contribution

It offers a quantitative analysis of RGW effects on pulsar timing, corrects RGW normalization using CMB data, and derives new observational constraints from pulsar timing arrays.

Findings

RGWs can produce detectable timing residuals if sufficiently strong.

Normalization of RGWs is reduced by two orders of magnitude after CMB correction.

New constraints on RGWs are obtained from Parkes Pulsar Timing Array data.

Abstract

Relic gravitational waves (RGWs) , a background originated during inflation, would give imprints on the pulsar timing residuals. This makes RGWs be one of important sources for detection using the method of pulsar timing. In this paper, we discuss the effects of RGWs on the single pulsar timing, and give quantitively the timing residuals caused by RGWs with different model parameters. In principle, if the RGWs are strong enough today, they can be detected by timing a single millisecond pulsar with high precision after the intrinsic red noise in pulsar timing residuals were understood, even though observing simultaneously multiple millisecond pulsars is a more powerful technique in extracting gravitational wave signals. We corrected the normalization of RGWs using observations of the cosmic microwave background (CMB), which leads to the amplitudes of RGWs being reduced by two orders of magnitude or so compared to our previous works. We made new constraints on RGWs using the recent observations from the Parkes Pulsar Timing Array, employing the tensor-to-scalar ratio $r=0.2$ due to the tensor-type polarization observations of CMB by BICEP2 as a referenced value even though it has been denied. Moreover, the constraints on RGWs from CMB and BBN (Big Bang nucleosynthesis) will also be discussed for comparison.