Two Top Utilities of Two Higgs Doublets: Electroweak Baryogenesis and Alignment

TL;DR

This paper explores how two Higgs doublets without a Z2 symmetry can naturally facilitate electroweak baryogenesis, produce observable flavor and CP violation, and explain the Higgs alignment phenomenon, predicting new sub-TeV Higgs states.

Contribution

It demonstrates that without Z2 symmetry, new complex top Yukawa couplings enable efficient baryogenesis and naturally lead to Higgs alignment, predicting accessible exotic Higgs bosons.

Findings

Electroweak baryogenesis is efficient with order-one couplings.

The observed Higgs alignment arises naturally in this framework.

Exotic Higgs bosons are predicted to be sub-TeV, accessible at the LHC.

Abstract

With two Higgs doublets but without any discrete $Z_2$ symmetry to forbid flavor changing neutral Higgs couplings, new top Yukawa couplings $\rho_{tt}$ and $\rho_{tc}$ are allowed and naturally complex. Electroweak baryogenesis is remarkably efficient if both $\rho_{tt}$ (and $\rho_{tc}$) and exotic Higgs quartic couplings are ${\cal O}(1)$. Furthermore, the alignment phenomenon, that the observed 125 GeV boson so closely resembles the Standard Model Higgs boson, emerges naturally. One not only has many new flavor and CPV phenomena (modulo SM-like flavor organization plus alignment), but the exotic Higgs bosons $H^0$, $A^0$ and $H^+$ are necessarily sub-TeV in mass, and LHC search should be readjusted.