Abstract
Primordial gravitational waves provide a very important stochastic background that could be detected soon with interferometric gravitational wave antennas or indirectly via the induced patterns in the polarization anisotropies of the cosmic microwave background. The detection of these waves will open a new window into the early Universe, and therefore it is important to characterize in detail all possible sources of primordial gravitational waves. In this paper we develop theoretical and numerical methods to study the production of gravitational waves from out-of-equilibrium gauge fields at preheating. We then consider models of preheating after hybrid inflation, where the symmetry breaking field is charged under a local $U(1)$ symmetry. We analyze in detail the dynamics of the system in both momentum and configuration space. We show that gauge fields leave specific imprints in the resulting gravitational wave spectra, mainly through the appearance of new peaks at characteristic frequencies that are related to the mass scales in the problem. We also show how these new features in the spectra correlate with stringlike spatial configurations in both the Higgs and gauge fields that arise due to the appearance of topological winding numbers of the Higgs around Nielsen-Olesen strings. We study in detail the time evolution of the spectrum of gauge fields and gravitational waves as these strings evolve and decay before entering a turbulent regime where the gravitational wave energy density saturates.
Highlights
Gravitational waves (GW) are a robust prediction of General Relativity [1]
Among the backgrounds of cosmological origin, we find the approximately scale-invariant background produced during inflation [3], or the gravitational wave background (GWB) generated at hypothetical early universe thermal phase transitions [4,5,6,7], from relativistic motions of turbulent plasmas [8] or from the decay of cosmic strings [1]
A IR peak appears first, when bubbles of the Higgs start to collide and strings are formed in between the bubbles. The frequency of this IR peak tends to be smaller than the frequency of the peak of the GW spectrum produced without gauge field, but our results indicate that it varies in the same way with the model parameters
Summary
Gravitational waves (GW) are a robust prediction of General Relativity [1]. They correspond to ripples in spacetime that travel at the speed of light, and are typically produced whenever an astronomically large body of mass moves at relativistic speeds like in astrophysical binary systems, or whenever large density contrast waves collide against each other, like in early universe phase transitions. Among the backgrounds of cosmological origin, we find the approximately scale-invariant background produced during inflation [3], or the GWB generated at hypothetical early universe thermal phase transitions [4,5,6,7], from relativistic motions of turbulent plasmas [8] or from the decay of cosmic strings [1]. The detailed calculations show that the amplitude of this new GW background is two orders of magnitude greater than that expected from inflation for the same energy scale [19], and might be detected directly by the future GW detectors or in the B-mode polarization of the CMB [20] Another source of GW that may be relevant for interferometric experiments and whose study will be our main target here, is provided by the violent period following the end of inflation. The details of our lattice calculation are given in appendix B
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