Setting up stasis with gravitational interactions

TL;DR

This paper explores how gravitational interactions can establish initial conditions for cosmological stasis, a phase where matter and radiation components maintain a constant effective equation of state, through black hole evaporation and inflationary particle production.

Contribution

It demonstrates that primordial black hole evaporation and inflationary gravitational particle production can set up initial conditions for cosmological stasis, predicting distinctive particle abundance scaling laws.

Findings

Both scenarios can produce viable initial conditions for stasis.

Distinctive scaling exponents for particle abundance are predicted.

The models support the feasibility of cosmological stasis in the early Universe.

Abstract

An epoch known as cosmological stasis may have taken place in the early Universe. During matter-radiation stasis, a population of non-relativistic particles with different masses gradually decay into relativistic particles, and the effective equation of state $w$ remains approximately constant at a value between that of matter ($w=0$) and that of radiation ($w=1/3$). In this work, we investigate how to set up the appropriate initial conditions for stasis using gravitational interactions. We consider two scenarios: that the tower of non-relativistic particles is populated by the evaporation of primordial black holes (PBHs) and that the tower is populated by cosmological gravitational particle production (CGPP) during inflation. We calculate the abundance of particles on different levels of the tower to assess whether stasis is viable. We find that both scenarios can provide the needed initial conditions for stasis, and that they predict distinctive scaling exponents $\Omega_l \propto m_l^\alpha$ with mass $m_l$.