Gravitational wave production from preheating: parameter dependence

摘要

Parametric resonance is among the most efficient phenomena generating gravita-tional waves (GWs) in the early Universe. The dynamics of parametric resonance, and hence of the GWs, depend exclusively on the resonance parameter q. The latter is determined by the properties of each scenario: the initial amplitude and potential curvature of the oscillating ?eld, and its coupling to other species. Previous works have only studied the GW production for ?xed value(s) of q. We present an analytical derivation of the GW amplitude dependence on q, valid for any scenario, which we confront against numerical results. By running lattice simulations in an expanding grid, we study for a wide range of q values, the production of GWs in post-in?ationary preheating scenarios driven by parametric resonance. We present simple ?ts for the ?nal amplitude and position of the local maxima in the GW spectrum. Our parametrization allows to predict the location and amplitude of the GW background today, for an arbitrary q. The GW signal can be rather large, as h~2 Ω_(GW)(f_p) ≤ 10-11 , but it is always peaked at high frequencies f_p & 10~7 Hz. We also discuss the case of spectator-?eld scenarios, where the oscillatory ?eld can be e.g. a curvaton, or the Standard Model Higgs.