A new gravitational wave background from the Big Bang

TL;DR

This paper models the generation of a stochastic gravitational wave background during the universe's reheating phase after hybrid inflation, highlighting potential detectability and implications for early universe physics.

Contribution

It introduces a detailed mechanism for gravitational wave production during reheating, including bubble collisions and turbulence, and assesses their detectability across different inflation scales.

Findings

Significant gravitational wave energy density possible at GUT scales

Low-scale models may produce detectable signals for BBO or DECIGO

Similar results obtained for chaotic inflation models

Abstract

The reheating of the universe after hybrid inflation proceeds through the nucleation and subsequent collision of large concentrations of energy density in the form of bubble-like structures moving at relativistic speeds. This generates a significant fraction of energy in the form of a stochastic background of gravitational waves, whose time evolution is determined by the successive stages of reheating: First, tachyonic preheating makes the amplitude of gravity waves grow exponentially fast. Second, bubble collisions add a new burst of gravitational radiation. Third, turbulent motions finally sets the end of gravitational waves production. From then on, these waves propagate unimpeded to us. We find that the fraction of energy density today in these primordial gravitational waves could be significant for GUT scale models of inflation, although well beyond the frequency range sensitivity of gravitational wave observatories like LIGO, LISA or BBO. However, low-scale models could still produce a detectable signal at frequencies accessible to BBO or DECIGO. For comparison, we have also computed the analogous background from some chaotic inflation models and obtained similar results to those of other groups. The discovery of such a background would open a new observational window into the very early universe, where the details of the process of reheating could be explored. Thus, it could also serve as a new experimental tool for testing the Inflationary Paradigm.