Status of the Charged Higgs Boson in Two Higgs Doublet Models

Abstract: The existence of charged Higgs boson(s) is inevitable in models with two (or more) Higgs doublets. Hence, their discovery would constitute unambiguous evidence for new physics beyond the Standard Model (SM). Taking into account all relevant results from direct charged and neutral Higgs boson searches at LEP and the LHC, as well as the most recent constraints from flavour physics, we present a detailed analysis of the current phenomenological status of the charged Higgs sector in a variety of well-motivated Two Higgs Doublet Models (2HDMs). We find that charged Higgs bosons as light as 75 GeV can still be compatible with the combined data, although this implies severely suppressed charged Higgs couplings to all fermions. In more popular models, e.g. the 2HDM of Type II, we find that flavour physics observables impose a combined lower limit on the charged Higgs mass of M_H+ > 600 GeV - independent of tan(beta) - which increases to M_H+ > 650 GeV for tan(beta) < 1. We furthermore find that in certain scenarios, the signature of a charged Higgs boson decaying into a lighter neutral Higgs boson and a W boson provides a promising experimental avenue that would greatly complement the existing LHC search programme for charged Higgs boson(s).

• The paper presents a comprehensive analysis of charged Higgs constraints in 2HDMs using collider and flavor physics data.
• Key findings reveal viable charged Higgs masses as low as 75 GeV and robust lower limits near 600 GeV in Type II models.
• The study identifies promising decay channels, such as H± → W±h, as essential targets for future experimental searches.

Overview of the Two Higgs Doublet Models and Charged Higgs Boson

The paper explores the intricate landscape of Two Higgs Doublet Models (2HDMs), particularly focusing on the status and constraints associated with the charged Higgs boson. The discovery of a charged Higgs boson would provide compelling evidence for new physics beyond the Standard Model (SM), as 2HDMs naturally predict their existence when more than one Higgs doublet is introduced. This analysis leverages comprehensive data from direct searches at LEP and the LHC, alongside constraints from flavor physics, to evaluate the current phenomenological stance of charged Higgs bosons across different 2HDM types.

Key numerical findings have been emphasized for clarity. Charged Higgs bosons as light as 75 GeV remain viable within the constraints of experimental data, though this necessitates notably suppressed couplings to fermions. Furthermore, the 2HDM Type II model imposes a robust lower limit on the charged Higgs mass of approximately 600 GeV, invariant to the parameter $\tan\beta$, and extending to around 650 GeV for $\tan\beta < 1$.

Experimental constraints from collider searches are potent yet significantly affected by the coupling structure of the Higgs bosons in 2HDMs. The analysis incorporates results from processes sensitive to both light and heavy charged Higgs bosons, considering their decay channels into $\tau\nu$, $cs$, and $tb$ final states. The paper underscores that direct searches at LEP provide a lower bound of 80 GeV on the mass, although recent LHC data suggest stronger constraints at certain $\tan\beta$ values. Intriguingly, the decay mode $H^\pm \to W^\pm h$ manifests as a promising avenue for future experimental searches, offering complementary constraints on the charged Higgs sector.

Flavor physics plays an instrumental role in establishing limits far beyond the reachable scales of direct searches, effectively restricting the parameter space. Observables such as $\mathrm{BR}(B\to X_s\gamma)$ impose substantial constraints, particularly for 2HDM Types II and III, where a $\tan\beta$-independent lower bound on the mass arises. Additionally, other flavor observables, including $B\to D^{(*)}\ell\nu$ and $B_u\to\tau\nu$, are analyzed to further explore parameter compatibilities, notably stressing the challenges posed by current deviation observations involving these decays.

Theoretical and practical implications underscore the profound impact of charged Higgs discovery on our understanding of Higgs sector extensions. While the paper refrains from sensational claims, it sets a clear narrative about the gains in precision and the constraints it extends into the science of the Higgs sector. By dissecting various scenarios, including \textit{MSSM-like}, \textit{decoupling regime}, and \textit{generic couplings}, the research reflects on both established theories and experimental data, looking into potential future developments and the pursuit of verifying new physics models.

Finally, potential developments in AI might influence the data analysis processes or simulations employed within such extensive studies. Enhancing cross-disciplinary approaches could facilitate more comprehensive investigations, as AI methods increasingly play roles in optimizing experimental design and reducing computational overheads for complex simulations.

This paper stands as a cohesive inquiry into the status of charged Higgs sectors, delineating both robust and contentious areas of the 2HDM parameter space while suggesting avenues for future exploration.