Multi-Higgs boson signals of a modified muon Yukawa coupling at a muon collider

Abstract

We study di-Higgs and tri-Higgs boson productions at a muon collider as functions of the modification of the muon Yukawa coupling resulting from new physics parametrized by the dimension-six mass operator. We show that the di-Higgs signal can be used to observe a deviation in the muon Yukawa coupling at the 10% level for s=10  TeV and at the 3.5% level for s=30  TeV. The tri-Higgs signal improves the sensitivity dramatically with increasing s, reaching 0.8% at s=30  TeV. We also study all processes involving Goldstone bosons originating from the same operator, discuss possible model dependence resulting from other operators of dimension-six and higher, and identify μ+μ−→hh, μ+μ−→hhh, and μ+μ−→hZLZL as golden channels. We further extend the study to an effective field theory including two Higgs doublets with type-II couplings and show that di-Higgs and tri-Higgs signals involving heavy Higgs bosons can be enhanced in the alignment limit by a factor of (tanβ)4 and (tanβ)6, respectively, which results in the potential sensitivity to a modified muon Yukawa coupling at the 10−6 level already at a s=10  TeV muon collider. The results can easily be customized for other extensions of the Higgs sector. Published by the American Physical Society 2024