Lepton Flavor-Violating Higgs Decays Mediated by Ultralight Gauge Boson

Abstract

We present an analysis of the lepton-flavor violating decay of the Higgs boson mediated by an ultralight gauge boson, $\chi$. Our analysis matches a model generating the lepton flavor-violating interaction ${\bar{\ell }}_i{\ell }_j\chi$ at tree level with an effective field theory, safeguarding a physical massless $\chi$-boson limit of the observables. By utilizing the upper bounds on $H\to {\ell }_i{\bar{\ell }}_j$ decays from CMS and ATLAS Collaborations, we establish an indirect upper limit on the nonstandard decay $H\to {\ell }_i{\bar{\ell }}_j\chi$. The analysis encompasses various observables such as the lepton energy spectrum, Dalitz plot distribution, and Lepton Charge and Forward-Backward Asymmetries.

Comments: 19 pages, 8 figures. Extended discussion. Matches published version