If they do not thermalise quickly, generic inflationary models with become highly inhomogeneous if there is a long matter-dominated phase following the end of inflation. We compute the gravitational wave signal generated by the simplest models. We show that with extreme parameter choices the resulting background would be observable in next-generation detectors. Moreover, we speculate that more realistic models can generate larger backgrounds.
Abstract
Following inflation, the Universe may pass through an early matter-dominated phase supported by the oscillating inflaton condensate. Initially small fluctuations in the condensate grow gravitationally on subhorizon scales and can collapse to form nonlinear “inflaton halos”. Their formation and subsequent tidal interactions will source gravitational waves, resulting in a stochastic background in the present Universe. We extend N-body simulations that model the growth and interaction of collapsed structures to compute the resulting gravitational wave emission. The spectrum of this radiation is well-matched by semi-analytical estimates based on the collapse of inflaton halos and their tidal evolution. We use this semi-analytic formalism to infer the spectrum for scenarios where the early matter-dominated phase gives way to a thermalized universe at temperatures as low as 100MeV and we discuss the possible experimental opportunities created by this signal in inflationary models in which thermalization takes place long after inflation has completed.
- Eggemeier, Niemeyer, Jedamzik and Easther
- Stochastic Gravitational Waves from Post-inflationary Structure Formation
- Phys.Rev.D 107 (2023) 4, 043503 or ArXiV:2212.00425
Stochastic gravitational wave background expected from nonlinear dynamics after the simplest models of inflation, as a function thermalisation temperature.