Impact of hidden heavy Higgs channels of VLB-Quarks below 1 TeV in 2HDM

Abstract

We investigate the phenomenological impact of incorporating vector-like bottom (VLB) quarks into the Type-II Two-Higgs-Doublet Model (2HDM-II). This framework introduces novel beyond-Standard-Model (BSM) decay channels $B\to Hb$, $B\to Ab$, and $B\to H^{-}t$, which are typically ignored by LHC pair-production searches focused on Standard Model (SM) final states ($B\to Zb$, $B\to hb$, $B\to Wt$). Our analysis reveals that these BSM pathways significantly weaken current VLB mass constraints. In the 2HDM-II alignment limit, the mass limit for a singlet $B$ shifts from approximately 1.5 TeV down to 1.34 TeV. For $(T,B)$ and $(B,Y)$ doublet configurations, the mass limits relax further to approximately 0.98 TeV, driven by the dominance of $B\to Hb$ and $B\to Ab$ decays, which can reach combined branching ratios of nearly 100\%.