Strongly Magnetized Hot QCD Matter and Stochastic Gravitational Wave Background

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 ($h^2 Ω_{gw}$). 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.