Stochastic Background of Gravitational Waves from Hybrid Preheating

The process of reheating the Universe after hybrid inflation is extremely violent. It proceeds through the nucleation and subsequent collision of large concentrations of energy density in bubblelike structures, which generate a significant fraction of energy in the form of gravitational waves. We study the power spectrum of the stochastic background of gravitational waves produced at reheating after hybrid inflation. We find that the amplitude could be significant for high-scale models, although the typical frequencies are well beyond what could be reached by planned gravitational wave observatories. On the other hand, low-scale models could still produce a detectable stochastic background at frequencies accessible to those detectors. The discovery of such a background would open a new window into the very early Universe.

Figure 1

The time evolution of the different types of energy, normalized to the initial vacuum energy, for a model with $v={10}^{-3}{M}_P$. There are three well characterized stages: tachyonic growth, bubble collisions, and turbulence.

Figure 2

The comparison between the GW power spectrum obtained with increasing lattice resolution, to prove the robustness of our method. The different realizations are characterized by the number of lattice points ($N$), the minimum lattice momentum ($p_{\min }$), and the lattice spacing (ma). The growth is shown in steps of $m\Delta t=1$ for the lower spectra and $m\Delta t=5$ for the rest.

Figure 3

The sensitivity of the different gravitational wave experiments, present and future, compared with the possible stochastic backgrounds; we include the white dwarf binaries (WDB) [26] and chaotic preheating ($\lambda {\varphi }^4$) [10] for comparison.