Rescuing High-Scale Leptogenesis using Primordial Black Holes

TL;DR

This paper investigates how primordial black holes can enable high-scale leptogenesis by providing a late-time source of right-handed neutrinos, overcoming washout constraints present in standard cosmology.

Contribution

It introduces a novel scenario where light primordial black holes facilitate leptogenesis at high scales, expanding viable parameter space beyond standard limits.

Findings

Primordial black holes can produce right-handed neutrinos via Hawking radiation.

PBH-assisted leptogenesis allows high-scale neutrino masses to generate baryon asymmetry.

The viable parameter space for leptogenesis is significantly extended with PBH involvement.

Abstract

We explore the interplay between light primordial black holes (PBH) and high-scale baryogenesis, with a particular emphasis on leptogenesis. We first review a generic baryogenesis scenario where a heavy particle, $X$, with mass, $M_X$, produced solely from PBH evaporation decays to generate a baryon asymmetry. We show that the viable parameter space is bounded from above by $M_X \lesssim 10^{17}$ GeV and increases with decreasing $M_X$. We demonstrate that regions of the leptogenesis parameter space where the lightest right-handed neutrino (RHN) mass $M_{N_{1}}\gtrsim 10^{15}\,{\rm GeV}$ and neutrino mass scale $m_\nu\gtrsim 0.1$ eV, excluded in standard cosmology due to $\Delta L=2$ washout processes, becomes viable with the assistance of light PBHs. This scenario of PBH-assisted leptogenesis occurs because the PBHs radiate RHNs via Hawking evaporation late in the Universe's evolution when the temperature of the thermal plasma is low relative to the RHN mass. Subsequently, these RHNs can decay and produce a lepton asymmetry while the washout processes are suppressed.