Gravitational wave spectra from oscillon formation after inflation

Abstract

We systematically investigate the preheating behavior of single field inflation with an oscillon-supporting potential. We compute both the properties of the emitted gravitational waves as well as the number density and characteristics of the produced oscillons. By performing numerical simulations for a variety of potential types, we divide the analyzed potentials in two families, each of them containing potentials with varying large- or small-field dependence. We find that the shape of the spectrum and the amplitude of emitted gravitational waves have a universal feature with the peak around the physical wavenumber k/a ∼ m at the inflaton oscillation starting period, irrespective of the exact potential shape. This can be used as a smoking-gun for deducing the existence of a violent preheating phase and possible oscillon formation after inflation. Despite this apparent universality, we also find differences in the shape of the spectrum of emitted gravitational waves between the two families of potentials, leading to discriminating features between them. In particular, all potentials show the emergence of a two-peak structure in the gravitational wave spectrum, arising at the time of oscillon formation. However, potentials that exhibit efficient parametric resonance tend to smear out this structure and by the end of the simulation the two-peak structure is replaced by one broad peak in the GW spectrum. We further compute the number density and properties of the produced oscillons for each potential choice, finding differences in the number density and size distribution of stable oscillons and transient overdensities. We also perform a linear fluctuation analysis and use the corresponding Floquet charts to relate the results of our simulations to the structure of parametric resonance for the various potential types. We find that the growth rate of the scalar perturbations and the associated oscillon formation time are sensitive to the small-field shape of a potential while the macroscopic physical properties of oscillons such as the total number depend on the large-field shape of a potential.

Challenges and opportunities of gravitational-wave searches at MHz to GHz frequencies

“…Oscillon production Oscillons are long-lived compact objects (Gleiser 1994) that can be formed in the early Universe in a variety of post-inflationary scenarios which involve a preheating-like phase (Amin and Shirokoff 2010;Amin et al , 2012Zhou et al 2013;Amin 2013;Lozanov and Amin 2014;Antusch et al 2017Antusch et al , 2018aLozanov and Amin 2018;Amin et al 2018;Antusch et al 2019;Sang and Huang 2019;Lozanov and Amin 2019;Fodor 2019;Hiramatsu et al 2021). Their dynamics is a possible source of GW production.…”

Polarized Vector Oscillons

“…They have been realized in a broad variety of contexts in nature, from water waves [1] to Bose-Einstein condensates (BEC) [2][3][4][5]. They might also play a role in astrophysics and cosmology, with novel signatures in phase transitions in the early universe [6][7][8][9][10], in the formation of structure and gravitational clustering [11][12][13][14][15][16], production of gravitational waves [17][18][19][20][21][22][23][24][25] and electromagnetic radiation [26][27][28][29], formation of black holes [30][31][32][33][34], and even play a role in baryogenesis [35,36]. While massive scalar fields and their solitons have been explored in detail in the literature, Nature provides us with many examples of higher spin fields.…”

Vacuum bubble collisions: From microphysics to gravitational waves

“…A possible dynamical feature that we have not fully explored is the presence or absence of oscillons [75,76]: long-lived, localised nonlinear structures in the scalar field. Their existence, abundance and longevity depend on the form of the microphysical potential, and they in turn may contribute to the production of gravitational waves [77,78]. However, a static oscillon produced at z = 0 would break the two boost symmetries of O(2, 1), essentially because it is of an approximately fixed size, and not growing continuously.…”