Long-lived particle phenomenology in the 2HDM+$a$ model

• Main Authors: Haisch, Ulrich, Schnell, Luc
• Format: Journal Article
• Language: English
• Published: 10-05-2023
• Subjects: Physics - High Energy Physics - Experiment; Physics - High Energy Physics - Phenomenology
• DOI: 10.48550/arxiv.2302.02735

JHEP 04 (2023) 134 Higgs decays displaced from the primary interaction vertex represent a
striking experimental signature that is actively searched for by the ATLAS, CMS
and LHCb collaborations. We point out that signals of this type appear in the
context of the 2HDM+$a$ model if the mixing angle $\theta$ of the two CP-odd
weak spin-0 eigenstates is tiny and the dark matter (DM) sector is either
decoupled or kinematically inaccessible. Utilising two suitable benchmark
scenarios, we determine the constraints on the parameter space of the 2HDM+$a$
model that are set by the existing LHC searches for long-lived particles (LLPs)
in Higgs decays. We find that depending on the precise mass spectrum of the
spin-0 states, mixing angles $\theta$ in the ballpark of a few $10^{-8}$ to
$10^{-5}$ can be excluded based on LHC Run II data. This finding emphasises the
unique role that searches for displaced signatures can play in constraining the
parameter space of the 2HDM+$a$ model. The ensuing DM phenomenology is also
discussed. In particular, we show that parameter choices leading to an
interesting LLP phenomenology can simultaneously explain the DM abundance
observed in today's Universe.