Title: Gravitational wave signals from spectator scalar fields

Host: Csaba Csaki

Abstract: In this talk, I will present a mechanism for gravitational wave generation from spectator scalar fields in the early universe. Spectator scalar fields, lighter than the inflationary scale, can produce a large isocurvature power spectrum in the ultraviolet region, leading to significant curvature perturbations at small scales caused by fluctuations in the spectator fields. These large perturbations result in a stochastic gravitational wave background (SGWB), typically in the range Ω_GW h^2 = 10^{-18} – 10^{-13}, within a frequency range of 1 nHz to 1 kHz. Importantly, future gravitational wave observatories may detect such gravitational waves. Finally, I will discuss how the isocurvature power spectrum can be enhanced through direct coupling between the inflaton and spectator fields, or via the presence of nonminimal couplings.