Dark Contributions to h → μ⁺μ^– in the Presence of a μ-Flavored Vector-Like Lepton

A simple extension of the standard model (SM) with a μ-flavored vector-like lepton (VLL) doublet and a real singlet scalar can have an interesting implication to the h → μ⁺μ^– decay while offering the simplest possible explanation for the dark matter (DM) phenomenology. Assuming the real singlet scalar to be a viable DM candidate, it has been shown that the muon Yukawa coupling can have a negative contribution at the one-loop order if the 2^nd generation SM leptons are allowed to couple with the VLL doublet. The stringent direct detection bounds corresponding to a real singlet scalar DM can easily be relaxed if the SM quark sector was augmented with a dimension-6 operator at some new physics (NP) scale Λ_NP. Thus, this model presents a significant phenomenological study where the muon Yukawa coupling can be corrected within a real singlet scalar DM framework. The considered parameter space can be tested/constrained through the high luminosity run of the LHC (HL-LHC) and future direct detection experiments.