Baryon Asymmetry from a Composite Higgs Boson

Abstract

We study the nature of the electroweak phase transition (EWPT) in models where the Higgs boson 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 focuses 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 mesonlike 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 sizable 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 flavor and CP constraints. Our scenario can be tested in complementary ways: by measuring the CP-odd top Yukawa coupling in electron electric dipole moment experiments, by searching for dilaton production and deviations in Higgs couplings at colliders, and through gravitational waves at LISA.