Enhanced four-body decays of charged Higgs bosons into off-shell pseudoscalar Higgs and $$W^\pm $$ W ± boson pairs in a lepton-specific 2-Higgs doublet model

Abstract

Abstract We study the time-honoured decay $$H^\pm \rightarrow A W^\pm $$ H ± → A W ± but for the first time, we do so for the case of both A and $$W^\pm $$ W ± being off-shell, therefore computing a $$1\rightarrow 4$$ 1 → 4 body decay. We show that the corresponding decay rate not only extends the reach of $$H^\pm $$ H ± searches to small masses of the latter but also that the results of our implementation differ significantly from the yield of the $$1\rightarrow 3$$ 1 → 3 body decay over the phase space region in which the latter is normally used. We show the phenomenological relevance of this implementation in the case of the so-called lepton-specific 2-Higgs Doublet Model (2HDM) over the mass region wherein the aforementioned $$1\rightarrow 4$$ 1 → 4 body decay can dominate just beyond the top (anti)quark mass. This mass region is accessible in the lepton-specific 2HDM as the Yukawa couplings are such that limits from $$b \rightarrow s \gamma $$ b → s γ and $$\tau \rightarrow \mu \nu _{\tau } \bar{\nu _\mu }$$ τ → μ ν τ ν μ ¯ observables on $$M_{H^\pm }$$ M H ± are rather mild. However, we emphasize that similar effects may occur in other 2HDM types, as the $$W^\pm H^\mp A$$ W ± H ∓ A vertex is 2HDM type independent.