DW-genesis: baryon number from domain wall network collapse

TL;DR

This paper investigates how collapsing axionic domain walls in the early universe can generate the observed baryon asymmetry through spontaneous baryogenesis, analyzing different models and phenomenological signals like gravitational waves.

Contribution

It systematically studies baryon asymmetry production via domain wall collapse across various models, highlighting conditions for maximized asymmetry and addressing cancellation effects.

Findings

Baryon asymmetry peaks when domain walls collapse near interaction decoupling.

Gravitational wave signals from domain wall annihilation are potentially detectable.

Cancellation effects can suppress asymmetry, but methods to mitigate this are discussed.

Abstract

Axionic domain walls, as they move through the early universe plasma during their collapse, can generate a net baryon and lepton number through the mechanism of spontaneous baryogenesis, provided that there is a coupling between the axion and the lepton or baryon current. In this paper, we study systematically the baryon asymmetry produced by these domain walls (DWs) at annihilation, within different realisations of the $L$- or $B$-violating sector, and refer to this process as DW-genesis. We find that the baryon number is maximised when the DW network collapses approximately at the moment when the $L$- or $B$-violating interaction decouples. We study a model of minimal leptogenesis, a model of cogenesis, a model of baryogenesis and finally the possibility that the baryon asymmetry is produced by electroweak sphalerons. As phenomenological consequences of DW-genesis, we discuss the expected gravitational wave signal from the DW network annihilation and the prospects for detecting it. However, we finally emphasize that in realisations of the DW-genesis in minimal post-inflationary scenarios, there is a suppression induced by the cancellation between the asymmetry created by "opposite" axionic domain walls attached to the string. We quantify the impact of this cancellation and discuss possible ways to avoid it.