Can the Baryon Asymmetry Arise From Initial Conditions?

TL;DR

This paper explores whether initial conditions in an inflationary universe can explain the baryon asymmetry, finding it theoretically possible with specific conditions but requiring fine-tuning and careful model considerations.

Contribution

It demonstrates that baryon asymmetry from initial conditions is feasible under certain conditions, challenging the notion that inflation erases such initial asymmetries.

Findings

Initial conditions can produce baryon asymmetry with a light bosonic field.

Achieving this requires hyper-Planckian field displacements and tuned parameters.

Potential observable effects in double beta decay spectrum.

Abstract

In this letter, we quantify the challenge of explaining the baryon asymmetry using initial conditions in a universe that undergoes inflation. Contrary to lore, we find that such an explanation is possible if net $B-L$ number is stored in a light bosonic field with hyper-Planckian initial displacement and a delicately chosen field velocity prior to inflation. However, such a construction may require extremely tuned coupling constants to ensure that this asymmetry is viably communicated to the Standard Model after reheating; the large field displacement required to overcome inflationary dilution must not induce masses for Standard Model particles or generate dangerous washout processes. While these features are inelegant, this counterexample nonetheless shows that there is no theorem against such an explanation. We also comment on potential observables in the double $\beta$-decay spectrum and on model variations that may allow for more natural realizations.