The Baryon Asymmetry from a Composite Higgs

TL;DR

This paper explores a composite Higgs model where the electroweak phase transition is strongly first-order and can generate the baryon asymmetry, with testable predictions in collider experiments, EDM measurements, and gravitational waves.

Contribution

It introduces a novel analysis of the electroweak phase transition involving the confinement of a strong sector and the dilaton, linking it to baryogenesis and observable signals.

Findings

EWPT can be strongly first-order due to the nearly-conformal dilaton potential.

Varying top Yukawa coupling provides sufficient CP violation for baryogenesis.

Model predicts detectable signals in EDM experiments, collider deviations, and gravitational waves.

Abstract

We study the nature of the electroweak phase transition (EWPT) in models where the Higgs emerges as a pseudo-Nambu-Goldstone boson of an approximate global symmetry of a new strongly-interacting sector confining around the TeV scale. Our analysis focusses for the first time on the case where the EWPT is accompanied by the confinement phase transition of the strong sector. We describe the confinement in terms of the dilaton, the pseudo-Nambu-Goldstone boson of spontaneously broken conformal invariance of the strong sector. The dilaton can either be a meson-like or a glueball-like state and we demonstrate a significant qualitative difference in their dynamics. We show that the EWPT can naturally be strongly first-order, due to the nearly-conformal nature of the dilaton potential. Furthermore, we examine the sizeable scale variation of the Higgs potential parameters during the EWPT. In particular, we consider in detail the case of a varying top quark Yukawa coupling, and show that the resulting CP violation is sufficient for successful electroweak baryogenesis. We demonstrate that this source of CP violation is compatible with existing flavour and CP constraints. Our scenario can be tested in complementary ways: by measuring the CP-odd top Yukawa coupling in electron EDM experiments, by searching for dilaton production and deviations in Higgs couplings at colliders, and through gravitational waves at LISA.