Interpreting Pulsar Timing Array data of Gravitational Waves with Ekpyrosis-Bouncing Cosmology

TL;DR

This paper explores how an Ekpyrosis-bouncing cosmology model with a blue-tilted gravitational wave spectrum can explain recent pulsar timing array observations of the stochastic gravitational wave background, aligning theory with data.

Contribution

The paper develops a concrete Ekpyrosis-bouncing cosmology model that can interpret PTA data without pathologies, analyzing tensor and scalar perturbations under current observational constraints.

Findings

The model produces a strongly blue-tilted GW spectrum compatible with PTA data.

Both tensor and scalar perturbations are consistent with current observations.

The model offers a viable alternative explanation for the observed SGWB.

Abstract

Recent pulsar timing array (PTA) experiments have reported strong evidence of the stochastic gravitational wave background (SGWB). If interpreted as primordial Gravitational Waves (pGWs), the signal favors a strongly blue-tilted spectrum. On the other hand, the Ekpyrosis-bouncing cosmology with a strongly blue-tilted GW spectrum, i.e., $n_T \simeq 2$, offers a potential explanation for the observed SGWB signal. In this paper, we construct a concrete Ekpyrosis-bouncing model, and show its capacity to intepret the PTA result without pathologies. Both tensor and scalar perturbations are analysed with constraints from the current observations.