Explaining Pulsar Timing Array Observations with Primordial Gravitational Waves in Parity-Violating Gravity

TL;DR

This paper proposes that a parity-violating gravity model can explain recent pulsar timing array observations through polarized primordial gravitational waves, offering new insights into inflation and gravity theories.

Contribution

It introduces a simple parity-violating gravity model that predicts polarized primordial gravitational waves consistent with PTA data, linking inflationary scenarios to observable signals.

Findings

Primordial gravitational waves can be strongly circularly polarized.

Predicted PGWs exhibit significant anisotropies in the PTA frequency band.

The model's predictions can be tested with PTA and CMB observations.

Abstract

The pulsar timing array (PTA) collaborations have recently suggested the presence of a gravitational wave background at nano-Hertz frequencies. In this paper, we explore potential inflationary interpretation of this signal within the context of a simple and health parity-violating gravity model termed the Nieh-Yan modified Teleparallel Gravity. Through this model, two inflationary scenarios are evaluated, both yielding significant polarized primordial gravitational waves (PGWs) that align well with the results from PTA observations. Furthermore, the resulting PGWs can display strong circular polarization and significant anisotropies in the PTA frequency band, which are distinct features to be verified by observations of both PTA and the cosmic microwave background.The detection of such a distinctive background of PGWs is expected to provide strong evidence supporting our scenarios and insights into inflationary dynamics and gravity theory.