Strongly Magnetized Hot QCD Matter and Stochastic Gravitational Wave Background

TL;DR

This paper investigates how strong magnetic fields during the QCD phase transition in the early Universe influence the stochastic gravitational wave background, potentially affecting detection prospects with future observatories.

Contribution

It introduces a magnetized hot QCD equation of state to estimate gravitational wave signals, highlighting the impact of magnetic fields on GW frequency and amplitude predictions.

Findings

Magnetic fields lower the peak GW frequency compared to ideal gas models.

Strain amplitudes remain comparable to ideal gas predictions.

Potential detectability of magnetized GW signals by SKA is suggested.

Abstract

The first-order phase transitions in the early Universe are one of the well-known sources which release the stochastic background of gravitational waves. In this paper, we study the contribution of an external static and strong magnetic field on the stochastic background of gravitational waves (GWs) expected during QCD phase transition. In the light of the strongly magnetized hot QCD equation of state which deviated from the ideal gas up to the one-loop approximation, we estimate two phenomenologically important quantities: peak frequency redshifted to today ($f_{\rm peak}$) and GW strain amplitude ($h^2 \Omega_{gw}$). The trace anomaly induced by the magnetized hot QCD matter around the phase transition generates the stochastic background of GW with peak frequencies lower than the ideal gas-based signal (around nHz). Instead, the strain amplitudes corresponding to the peak frequencies are of the same order of magnitude of the expected signal from ideal gas. This may be promising in the sense that although the strong magnetic field could mask the expected stochastic background of GWs by upgrading the frequency sensitivity of detectors in the future, the magnetized GW is expected to be identified. Faced with the projected reach of detectors EPTA, IPTA, and SKA, we find that for the tail of the magnetized GW signals there remains a mild possibility of detection as it can reach the projected sensitivity of SKA.