Probing Charged Higgs Bosons in the 2-Higgs Doublet Model Type-II with Vector-Like Quarks

We study the phenomenology of charged Higgs bosons (H^±) and Vector-Like Quarks (VLQs), denoted as T, the latter possessing a charge identical to the top quark one, within the framework of the Two Higgs Doublet Model Type-II (2HDM-II). Upon examining two scenarios, one featuring a singlet (T) (2HDM-II+(T)) and another a doublet (TB) (2HDM-II+(TB)), we discover that the presence of VLQs has a significant effect on the (pseudo)scalar sector of the 2HDM-II. In particular, this leads to a reduction in the strict constraint on the mass of the charged Higgs boson, which is imposed by B-physics observables, specifically B→ X_sγ. The observed reduction stems from modifications in the charged Higgs couplings to the Standard Model (SM) top and bottom quarks. Notably, the degree of this reduction varies distinctly between the singlet 2HDM+(T) and doublet 2HDM+(TB) scenarios. Additionally, our investigation extends to constraints imposed by the oblique parameters S and T on the VLQ mixing angles. Furthermore, to facilitate efficient exploration of the '2HDM-II+VLQ' parameter space, we present results on pair production of VLQs T (pp→ TT̅), followed by T→ H^± b and H^±→ tb decays, yielding a distinctive 2t4b final state. This investigation thus provides valuable insights guiding the search for extended Higgs and quark sectors at the Large Hadron Collider (LHC) at CERN.