Fermion Condensate Inflation, Dynamical Waterfall Mechanism and Primordial Black Holes

TL;DR

This paper proposes a fermion condensate inflation model driven by four-fermion interactions from spacetime torsion, leading to a natural end to inflation, formation of primordial black holes, and potential parity-violation signatures.

Contribution

It introduces a novel inflation mechanism based on fermion condensates and spacetime torsion, linking primordial black hole formation to parity-violating gravity.

Findings

Fermion condensate inflation can produce primordial black holes as non-topological solitons.

The model naturally incorporates a waterfall mechanism ending inflation via an axial chemical potential.

Connections to Chern-Simons gravity imply observable parity-violation signatures.

Abstract

Fermion condensate inflation, where inflation emerges from four-fermion interactions induced by spacetime torsion, removes the need for additional scalar fields beyond the Standard Model. In this framework, the fermion field can be decomposed into two distinguished sectors, each giving rise to bound states. After integrating out fermions, the bound fields play the roles of the inflaton and the auxiliary fields, resembling hybrid inflation with a waterfall mechanism. The inclusion of an axial chemical potential naturally introduces a mechanism to end inflation and trigger instant preheating. During the waterfall phase, the effective potential of the fermion condensate supports the formation of non-topological solitons such as Q-balls, which act as seeds of primordial black holes. This model is intrinsically connected to Chern-Simons gravity, which implies a parity-violating universe. Consequently, both the primordial black hole (PBH) dark-matter abundance and parity-violation signatures could provide observational tests of the model.