Eur. Phys. J. C (2024) 84: 737
https://doi.org/10.1140/epjc/s10052-024-13112-x

Regular Article - Theoretical Physics

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

¹ School of Physics and Astronomy, University of Southampton, SO17 1BJ, Southampton, UK
² Department of Physics and Astronomy, Uppsala University, Box 516, 751 20, Uppsala, Sweden
³ Center for High Energy Physics, Peking University, 100871, Beijing, China
⁴ School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, 100871, Beijing, China

^b muyuansong@pku.edu.cn

Received: 30 June 2023
Accepted: 6 July 2024
Published online: 24 July 2024

Abstract

We study the time-honoured decay $H^{\pm }\to A{W}^{\pm }$ but for the first time, we do so for the case of both A and $W^{\pm }$ being off-shell, therefore computing a $1\to 4$ body decay. We show that the corresponding decay rate not only extends the reach of $H^{\pm }$ searches to small masses of the latter but also that the results of our implementation differ significantly from the yield of the $1\to 3$ 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 $1\to 4$ 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 $b\to s\gamma$ and $\tau \to \mu {\nu }_{\tau }\overline{{\nu }_{\mu }}$ observables on $M_{H^{\pm }}$ are rather mild. However, we emphasize that similar effects may occur in other 2HDM types, as the $W^{\pm }{H}^{\mp }A$ vertex is 2HDM type independent.