Gravitational Waves and Primordial Black Holes produced by Dark Meta Stable Vacuum Decay

TL;DR

This paper explores how dark sector phase transitions from metastable vacua can produce gravitational waves and primordial black holes, with implications for dark matter, dark energy, and cosmological observations.

Contribution

It introduces a phenomenological model linking dark metastable vacuum decay to gravitational wave signals and black hole formation, considering cosmological constraints.

Findings

Gravitational wave spectrum peaks at 3.1 times the Hubble rate at transition

Peak amplitude of gravitational waves is approximately 1.5 times the photon energy density

Primordial black hole formation is suppressed by N_eff constraints

Abstract

Inspired by string theory and cosmological constant problem, it is plausible that the Universe's vacuum structure is characterized by a landscape of metastable vacua. The existence of dark matter and dark energy further suggests that the dark sector may inhabit its own "dark landscape". If the dark vacuum is metastable, bubbles of lower-energy phases can nucleate at an approximately constant rate. Because the Hubble expansion rate is monotonically non-increasing with cosmic time, such nucleation can eventually lead to percolation and completion of a dark-sector phase transition. In this work, we investigate the phenomenological consequences of this transition, focusing on the resulting stochastic gravitational-wave background and the potential formation of primordial black holes. We find that the gravitational wave spectrum peaks at $k_{\mathrm{peak}}=3.1 H_{\mathrm{PT}}$, with an amplitude $\Omega_{\mathrm{GW}}^{\mathrm{peak}}\simeq1.5 \Omega_\gamma(\Delta\rho/\rho_{\mathrm{tot}})^2$. Furthermore, the formation of primordial black holes is suppressed due to $\Delta N_{\mathrm{eff}}$ constraint.