Light charged Higgs boson with dominant decay to quarks and its search at LHC and future colliders

The possibility of a light charged Higgs boson $H^\pm$ that decays predominantly to quarks ($cs$ and/or $cb$) and with a mass in the range 80 GeV $\le m_{H^\pm} \le 90$ GeV is studied in the context of Three-Higgs-Doublet Models (3HDMs). At present the Large Hadron Collider (LHC) has little sensitivity to this scenario, and currently the best constraints are from LEP2 and Tevatron searches. The branching ratio of $H^\pm\to cb$ can be dominant in two of the five types of 3HDM, and we determine the parameter space where this occurs. The decay $H^\pm\to cb$ has recently been searched for at the LHC for the first time, and with increased integrated luminosity one would expect sensitivity to the region 80 GeV $\le m_{H^\pm} \le 90$ GeV due to the smaller backgrounds with respect to $H^\pm\to cs$ decays.Comment: 25 pages, 17 figure

Investigation of the concurrent effects of ALP-photon and ALP-electron couplings in Collider and Beam Dump Searches

Axion-like particles (ALPs) have been studied in numerous experiments to search for their interactions, but most studies have focused on deriving bounds for the single coupling. However, in ultraviolet (UV) models, these couplings can appear simultaneously, and their interplay could have important implications for collider and beam dump searches. In this study, we investigate the concurrent effects of the ALP-photon and ALP-electron couplings in a simplified model and examine how their simultaneous presence modifies existing bounds. We find that modifications to production cross-sections, decaying branching ratios, and the lifetime of the ALP are the major effects. Our results show that low-energy electron-positron colliders such as Belle-II and BaBar are primarily affected by the first two factors, while beam dump experiments such as E137 and NA64 are affected by the cross sections and lifetime. We also consider two UV models - the KSVZ model and a lepton-specific version of the DFSZ model - which have only one of the two couplings at tree-level. However, the other coupling can be generated at loops, and our analysis reveals that the simultaneous presence of the two couplings can significantly modify existing bounds on these models for $10^{-3} < m_a < 10$ GeV, especially for beam dump experiments. Overall, our study highlights the importance of considering the concurrent effects of the ALP-photon and ALP-electron couplings in future collider and beam dump analyses.Comment: 29 pages, 11 figures; v2: matched to journal versio

Probing CP Violation in Dark Sector through the Electron Electric Dipole Moment

The Two Higgs Doublet Model (2HDM) stands as a promising framework for exploring physics beyond the Standard Model (SM). Within this context, we explore the possibility that the two Higgs doublets may serve as a window into CP-violating dark sectors, neutral under the SM gauge groups. Specifically, our focus is on investigating the electric dipole moment (EDM) of the electron, generated solely by CP violation in the dark sector. We present a general formula for the electron EDM, without specifying the structure of the dark sectors, and discuss the current constraints on various dark sector models. It is noteworthy that even in the case of a CP-conserving 2HDM, the resulting electron EDM is capable of reaching the current experimental limit, with CP violation arising exclusively from the dark sectors. Furthermore, we introduce a heavy dark sector (HDS) approximation for the analytic calculation of the EDM, assuming that the dark sector particles are much heavier than the physical states in the 2HDM. This approximation yields simplified analytic results that are consistent with the full numerical calculations.Comment: 46 pages, 8 figures, v2: some references and comments are adde

Slight excess at 130 GeV in search for a charged Higgs boson decaying to a charm quark and a bottom quark at the Large Hadron Collider

Searches for a charged Higgs boson ($H^\pm$) decaying to a charm quark and a bottom quark ($H^\pm \to cb$) have been carried out at the Large Hadron Collider (LHC) in the decay of top quarks ($t\to H^\pm b$). In a recent search by the ATLAS collaboration (with all Run II data, 139 fb$^{-1}$) a local excess of around $3\sigma$ has been observed, which is best fitted by a charged Higgs boson with a mass ($m_{H^\pm}$) of around 130 GeV and a product of branching ratios (BRs) given by BR$(t\to H^\pm b)\times{\rm BR}(H^\pm\to cb)=0.16\%\pm 0.06\%$. In the context of Two-Higgs-Doublet Models (2HDM) with independent Yukawa couplings for $H^\pm$ we present the parameter space for which this excess (assuming it to be genuine) can be accommodated, taking into account the limits from LHC searches for $H^\pm\to cs$ and $H^\pm\to \tau\nu$ at $m_{H^\pm}$=130 GeV and the constraint from $b\to s\gamma$. It is then shown that such an excess cannot be explained in 2HDMs with natural flavour conservation, but can be accommodated in the flipped Three-Higgs-Doublet Model (3HDM) and in the aligned 2HDM (A2HDM). Upcoming searches with 139 fb$^{-1}$ in the channels $H^\pm\to cb$ (CMS), $H^\pm \to cs$ (ATLAS/CMS) and $H^\pm \to \tau\nu$ (ATLAS/CMS) will determine if the excess is the first sign of an $H^\pm$ with $m_{H^\pm}=130$ GeV.Comment: 30 pages, 11 figure

An Investigation of Charged Higgs Phenomenology in 3HDM and its CP-violation Anomalies

In this thesis, we focus on the 3-Higgs-Doublets-Model (3HDM) with 3 active Higgs doublets and study some of the features of its extended scalar structure. Specifically, we investigate the phenomenology of the charged Higgs boson sector at both lepton and hadron colliders as well as in low energy experiments. By using LHC and LEP2 data, we study the properties of a CP-conserving light charged Higgs boson in its H±2 → cb decay channel. In order to detect this signature, we discuss the benefit of improved flavour tagging at both LEP2 and the LHC. In addition, we study three testable CP-violating asymmetry observables at the LHC and B factories, which could constrain the Yukawa couplings in the 3HDM when these are assumed complex only in the charged Higgs boson sector. Of particular interest is the untagged-asymmetry ACP(B¯ → Xs+dγ), a measurement of which at 2.5% or more could produce 5σ evidence for new physics that can be accommodated in such a 3HDM. Moreover, we evaluate the constraints on the charged Higgs boson sector from both BR(B¯ → Xsγ) and electron/neutron electric dipole moments (e/nEDMs), again, by assuming only a single CP-violating phase in the charged Higgs boson sector. In such a context, we illustrate a special GIM type cancellation mechanism entering the e/nEDMs, which is exact when the two physical charged Higgs bosons of the 3HDM (H±2and H±3) are strictly degenerate in mass but still enables interesting and viable new phenomenology with a mass difference up to the Electroweak (EW) scal

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

We study the time-honoured decay H-+/--&gt; AW(+/-) but for the first time, we do so for the case of both A and W-+/- being off-shell, therefore computing a 1 -&gt; 4 body decay. We show that the corresponding decay rate not only extends the reach of H-+/- searches to small masses of the latter but also that the results of our implementation differ significantly from the yield of the 1 -&gt; 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 -&gt; 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 -&gt; s gamma and tau -&gt;mu nu(tau)nu(mu)&lt;overline&gt; observables on MH +/- are rather mild. However, we emphasise that similar effects may occur in other 2HDM types, as the W(+/-)H(-/+)A vertex is 2HDM type independent

Revisiting for maximal flavor violating Z eμ ′ Zeμ′ {Z}_{e\mu}^{\prime } and its phenomenology constraints

Abstract Lepton flavor violation (LFV), observed conclusively in neutrino oscillations, remains a pivotal area of investigation due to its absence in the Standard Model (SM). Beyond the Standard Model (BSM) physics explores charged lepton flavor violation (CLFV), particularly through new particle candidates such as the Z ′. This article focuses on maximal LFV interactions facilitated by the Z ′ boson, specifically targeting its off-diagonal interactions with the first and second generations of charged and neutral leptons. In our ultraviolet (UV) model for the origin of the Z ′, inspired by the work of [R.Foot et al., Phys.Rev. D50 (1994) 4571-4580], we utilize the discrete Z 2 symmetry to investigate the maximal LFV mediated by the Z ′ between the muon (μ) and electron (e) arising from the additional scalars. This symmetry prohibits flavor-conserving interactions between Z ′ and μ + μ − , e + e − . In conjunction with collider, (g – 2) μ , (g – 2) e , inverse μ decay, Muonium-to-Antimuonium conversion and LFV decay constraints, we provide forecasts for anticipated limits derived from processes such as ν μ N → ν e μ + e − N in neutrino trident experiments like the DUNE search at the first time. These limits highlight the prospective scope and significance of LFV investigations within these experimental frameworks. Within the mass range of 0.01 GeV to 10 GeV, the most stringent limit arises from B μ → e + X + γ $$\mathcal{B}\left(\mu \to e+X+\gamma \right)$$ when M Z ′ < m μ $${M}_{Z^{\prime }}<{m}_{\mu }$$ , while ∆a e provides effective constraints as M Z ′ $${M}_{Z^{\prime }}$$ approaches 10 GeV. Looking ahead, the proposed Muonium-to-Antimuonium Conversion Experiment (MACE) is expected to impose the most stringent constraints on Muonium-to-Antimuonium oscillation, improving sensitivity by about one order of magnitude against ∆a e

Enhanced four-body decays of charged Higgs Bosons into off-shell pseudoscalar Higgs and W± Boson pairs in a lepton-specific 2-Higgs Doublet Model

We study the time-honoured decay H±→AW± but for the first time, we do so for the case of both A and W± being off-shell, therefore computing a 1→4 body decay. We show that the corresponding decay rate not only extends the reach of H± searches to small masses of the latter but also that the results of our implementation differ significantly from the yield of the 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→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→sγ and τ→μντνμ¯ observables on MH± are rather mild. However, we emphasise that similar effects may occur in other 2HDM types, as the W±H∓A vertex is 2HDM type independent

Light charged Higgs boson with dominant decay to a charm quark and a bottom quark and its search at LEP2 and future e+e- colliders

The possibility of a light charged Higgs boson H± that decays predominantly to a charm quark and a bottom quark (cb) and with a mass in the range 80  GeV≤MH±≤90  GeV is studied in the context of a three-Higgs doublet model (3HDM). Searches for this decay at the Large Hadron Collider do not have sensitivity to this mass region at present. It is shown that the searches for H± at LEP2 could be supplemented by either one or two b-tags, which would enable such large branching ratios for H±→cb to be probed in the above mass region. We comment on the possibility of this 3HDM scenario to explain a slight excess in the searches for H± at LEP2, which is best fit by MH± of around 90 GeV, and discuss the prospects for detecting H±→cb decays at future e+e− colliders