Flavor-Violating Higgs and Top Decays in the Type 1B Flavorful Two-Higgs-Doublet Model with a Twist

Abstract

We study flavor-violating decays of the SM-like Higgs boson and rare top decays in the Type 1B realization of the flavorful two-Higgs-doublet model with a twist, focusing on $h\to sb$, $h\to db$, $h\to uc$, $h\toμτ$, $h\to eτ$, $h\to eμ$, $t\to ch$, and $t\to uh$. We present the relevant amplitude and branching-ratio formulae, include one-loop vertex corrections, and impose constraints from Higgs signal-strength measurements, electroweak precision tests, meson mixing, $B\to X_sγ$, direct HFV searches and CLFV constraints, including $μ-e$ conversion. The surviving parameter space favors $\BR(h\to sb)\gg\BR(h\to db)$, $\BR(t\to ch)\gg\BR(t\to uh)$, and $\BR(h\toμτ)\gg\BR(h\to eτ)\sim\BR(h\to eμ)$ in the lepton sector. One-loop effects usually preserve these hierarchies, but can modify individual channels through different mechanisms: sizable destructive tree--loop interference can reduce $h\to sb$ enough to yield rare $\BR_{\mathrm{1L}}(h\to db)>\BR_{\mathrm{1L}}(h\to sb)$ points, whereas the large relative corrections found in rare top decays mainly reflect strong SM-like alignment suppressing the tree-level amplitudes.