Speaker
Description
In this work, we develop a generic formalism for the study of tensor perturbations induced at second order by first-order vector metric perturbations, dubbing these induced tensor modes vector-induced gravitational waves (VIGWs). Notably, considering an inflation-inspired power-law type magnetic field power spectrum of the form PB(k)∝knB (where nB is the magnetic spectral index), we show that the VIGW signal is enhanced for stiff post-inflationary EoS, with the maximum enhancement happening for w=1. We explicitly demonstrate this contribution is dominant over the first-order magnetically-sourced GWs. The VIGW spectrum exhibits a maximum at around the scale crossing the cosmological horizon at the end of reheating, kreh, with its present day peak amplitude scaling as ΩGW(kreh,η0)∝ΔNreh×(Hinf/MPl)8, where Hinf is the Hubble parameter at the end of inflation and ΔNreh the duration of the post-inflationary era in e-folds. For w=1 (kination) and nB>−3/2, one further obtains a nearly nB-independent frequency scaling of the GW spectrum of the form ΩGW(f,η0)∝(ffreh)−2.8 for f>freh≡kreh/(2π). Finally, we highlight that the VIGW signal can be well within the detection bands of several next-generation interferometric GW missions at small scales. Indicatively, for Hinf∼O(107)GeV and O(1014)GeV, and ΔNreh∼15 and 10, the VIGW signal is expected to be detectable by LISA and ET respectively.
Based on Ref: 2504.10477