Implications of the upper bound on $\boldsymbol{h\to\mu^+\mu^-}$ on the baryon asymmetry of the Universe

TL;DR

The paper discusses how experimental limits on Higgs decay to muons constrain the muon Yukawa coupling's role in generating the Universe's matter-antimatter imbalance, ruling out some scenarios but leaving others viable.

Contribution

It demonstrates that current bounds on Higgs to muon decays significantly restrict models where the muon Yukawa coupling causes baryon asymmetry, refining our understanding of matter-antimatter imbalance origins.

Findings

Bounds exclude muon Yukawa as dominant baryogenesis source.

Muon coupling can still contribute around 16% to baryon asymmetry.

Experimental constraints surpass previous CP-violation bounds.

Abstract

The upper bounds from the ATLAS and CMS experiments on the decay rate of the Higgs boson to two muons provide the strongest constraint on an imaginary part of the muon Yukawa coupling. This bound is more than an order of magnitude stronger than bounds from $\mathcal{CP}$-violating observables, specifically the electric dipole moment of the electron. It excludes a scenario $-$ which had been viable prior to these measurements $-$ that a complex muon Yukawa coupling is the dominant source of the baryon asymmetry. Even with this bound, the muon source can still contribute ${\cal O}(16\%)$ of the asymmetry.