Gravitational wave production from preheating: parameter dependence

Abstract

Parametric resonance is among the most efficient phenomena generating gravitational 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 field, and its coupling to other species. Previous works have only studied the GW production for fixed 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-inflationary preheating scenarios driven by parametric resonance. We present simple fits for the final 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-field scenarios, where the oscillatory field can be e.g. a curvaton, or the Standard Model Higgs.1 Note that this differs from the case of Higgs-Inflation [24,25], where the post-inflationary decay of the SM Higgs via parametric resonance [26][27][28][29], belongs to the context of preheating, as the Higgs rather plays there the role of the inflaton, instead of a spectator field.2 Note that we do not consider the case of 'oscillons', which correspond to stable field configurations formed whenever a field oscillates around the minimum of its potential, as long as the potential shape meets certain circumstances, see e.g. [54,55]. For the GW production from oscillons see [56,57].3 There exists nonetheless a parameter-fit analysis of the GW production in Hybrid preheating [49], but this corresponds to a spinodal instability of the daughter field modes, not to parametric resonance.

Production of gravitational waves during preheating with nonminimal coupling

“…Furthermore, the late time evolution of GW spectra leads to a minor peak in the low momentum region, which originates from the non-vanishing peak of the energy density spectrum of the inflaton quanta. For the case of a minimal coupling (ξ = 0), the peak value of GWs generated in the main resonance band is noticeably larger than those from subordinate bands, which is consistent with the result from the φ 4 chaotic inflation with an interaction between inflaton and a massless scalar field [9,28]. For the case of ξ = 0, one can see that there is a pronounced peak of GWs at the initial stage, which disappears completely in the final spectrum.…”

Gravitational wave forest from string axiverse

“…When some of the axions were located at plateau regions before they start to oscillate, significant amounts of GWs can be emitted in various frequency bands, corresponding to their mass scales (GW forest). Axions with f ∼ 10 16 GeV, which are typically predicted in string theory, lead to detectable GWs. This can open up a new window to probe string axiverse by means of future multi-band GW observations.…”

“…In Fig. 15, we chose the decay constant f as f = 10 16 GeV as is typically the case for stringy axions [7]. When we change f , Ω GW scales as Ω GW ∝ f 4 .…”

Reconstructing the spectral shape of a stochastic gravitational wave background with LISA

“…Furthermore, post-inflationary, early universe phenomena can also generate GWs with a large amplitude, e.g. a kination dominated phase [46][47][48][49][50], non-perturbative particle production phenomena [51][52][53][54][55][56][57][58][59][60][61][62], oscillon dynamics [63][64][65][66][67], strong first order phase transitions [68][69][70][71][72][73][74][75][76][77][78][79][80][81], or cosmic defect networks [82][83][84][85][86][87][88][89][90][91][92][93]. The resulting GW signal in such cases is given by the superposition of a very large number of uncorrelated and unresolved sources, and hence it is perceived by u...…”