arXiv subjects

Khiem Hong Phan

Publications and source records attributed to Khiem Hong Phan.

At least 19 recordsLinked to original sources

arXiv2026

Probing dark matter through charged Higgs pair production at future multi-TeV muon colliders: A machine-learning analysis

Probing dark matter (DM) via charged Higgs pair production at future multi-TeV muon colliders is investigated within the Inert Doublet Model (IDM). The viable parameter space of the IDM is first updated by incorporating theoretical constraints and current experimental data. Based on the allowed parameter space, we evaluate DM relic density and compare the results with the latest constraints from direct DM detection experiments. The resulting parameter points consistent with all DM constraints are subsequently employed to study charged Higgs pair production at future multi-TeV muon colliders, including the subsequent decays of the charged Higgs bosons into Standard Model (SM) particles in association with DM candidate. In particular, we study the following production processes: $μ^- μ^+ \to ν_μ \barν_μ H^{\pm} H^{\mp} \to \ell^+ \ell^- + ν_μ \barν_μ ν_{\ell} \barν_{\ell} HH$, $μ^- μ^+ \to ν_μ \barν_μ H^{\pm} H^{\mp} \to \ell^\pm + 2\,\text{jets} + ν_μ \barν_μ ν_{\ell} HH$ and $μ^- μ^+ \to ν_μ \barν_μ H^{\pm} H^{\mp} \to 4\,\text{jets} + ν_μ \barν_μ HH$ for $\ell =e, μ$. The signal significance is evaluated against the corresponding SM backgrounds using both cut-based and machine-learning (ML) approaches. We find that ML framework substantially enhances the sensitivity to the signal processes compared with the conventional cut-based analysis. Furthermore, our results indicate that the DM signals through charged Higgs pair production can be indirectly probed with a statistical significance exceeding $5σ$ for several viable benchmark points at future multi-TeV muon colliders.

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arXiv2026

Neutral scalar pair productions through $W$-boson fusion at multi--TeV muon colliders

Full one-loop electroweak radiative corrections to $μ^- μ^+ \to W^\pm W^\mp \to hh$ in the Standard Model are computed for the first time in this work. We then evaluate neutral scalar pair production through vector boson fusion at multi--TeV muon colliders within Two-Higgs-Doublet Model (THDM). In the phenomenological analysis, the enhancement factor, defined as the ratio of the cross sections for SM-like Higgs pair production in the THDM with respect to the corresponding ones in the SM, is examined over the viable regions of the parameter space in the Type-X and Type-Y THDMs. Our findings show that this ratio can reach a factor of $3$ in several regions within the valid parameter space of the Type-X THDM, whereas it ranges from $0.91$ to $0.96$ over the entire parameter space of the Type-Y THDM. Finally, we scan the cross sections for double CP-odd Higgs production over the updated parameter space of the Type-X and Type-Y THDMs. In the Type-Y case at $\sqrt{s} = 10$~TeV with an integrated luminosity of $\mathcal{L} = 10000~\text{fb}^{-1}$, CP-odd Higgs pair production in the $t\bar{t}b\bar{b}$ final state, with subsequent top-quark decays into leptons and bottom quarks taken into account, can be tested with a statistical significance exceeding the $2σ$ level at several viable parameter points.

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arXiv2025

Production of charged Higgs bosons associated with CP-even Higgs bosons at future multi--TeV muon colliders

We report the first results for charged Higgs boson production associated with CP-even Higgses at future multi--TeV muon colliders within the scenario of the Type-Y Two-Higgs-Doublet Model (THDM). The valid parameter regions in the Type-Y THDM are first updated, and based on the allowed parameter space, all two-body decay channels of the charged Higgs boson are then computed with the help of {\tt H-COUP}. Both production processes $μ^- μ^+ \to H^\pm H^\mp h, H^\pm H^\mp H \to t\bar{t} b\bar{b} h, t\bar{t} b\bar{b}H$ are scanned over the constrained parameter space of the considered model. The production cross sections can reach $\sim 0.5$ fb in several regions of the parameter space. The results provide an opportunity to probe charged Higgs bosons produced in association with the heavy CP-even Higgses at the high integrated luminosities proposed for future multi--TeV muon colliders. Furthermore, we evaluate the signal significances for $μ^- μ^+ \to H^\pm H^\mp h \to t\bar{t} b\bar{b} h \to t\bar{t} b\bar{b} b\bar{b}$ with respect to the Standard Model backgrounds. We also estimate the significances by including the top quark decay into leptons and bottom quarks and considering $b$-tagging. Thanks to the high integrated luminosities anticipated at future multi--TeV muon colliders,we find that the signal significances can exceed $\sim 3σ$ at several benchmark points selected in the viable parameter space of the Type-Y THDM.

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arXiv2025

Charged Higgs bosons associated with neutral gauge bosons at future multi--TeV muon colliders

The first results for charged Higgs pair production associated with neutral gauge bosons at future multi--TeV muon colliders are presented within the framework of the Two-Higgs-Doublet Model. In the phenomenological studies for the production processes, we first update the parameter space of the Type-X Two-Higgs-Doublet Model. From the viable regions of the parameter space, we compute the production cross sections, including all two-body decay modes of the charged Higgs boson. We mention that all two-body decay modes of the charged Higgs boson are evaluated with one-loop electroweak corrections, with two-loop QCD corrections also included for the decays of the charged Higgs into two fermions. The signal significances are also examined for several benchmark points within the updated parameter space. It is worth emphasizing that the production cross sections used for computing the significances in this work include initial-state radiation corrections up to two-loop order. With the help of the high integrated luminosity planned for future multi--TeV muon colliders, the production signals can be observed with a statistical significance exceeding $5σ$ for several selected points within the allowed parameter space.

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arXiv2025

One-loop expressions for $H^{\pm} \rightarrow W^{\pm} Z$ and their implications at muon--TeV colliders

One-loop contributions for decay process $H^{\pm} \rightarrow W^{\pm}Z$ within the Two-Higgs-Doublet Model are computed in the general $\mathcal{R}_ξ$ gauge, and its phenomenological applications at future muon--TeV colliders are studied in this paper. The analytic results are confirmed by several consistency tests, for example, the $ξ$-independence, the renormalization-scale stability and the ultraviolet finiteness of the one-loop amplitude. We first perform an updated parameter scan of the Type-X THDM in the phenomenological studies. The production of charged Higgs boson pairs at future muon--TeV colliders is investigated through the two processes $μ^+μ^- \rightarrow H^+H^- \rightarrow W^{\pm}W^{\mp}Zh$ and $μ^+μ^- \rightarrow γγ\rightarrow H^+H^- \rightarrow W^{\pm}W^{\mp}Zh$. Both signal events and their significances are evaluated with taking into account the corresponding Standard Model backgrounds. We find that the signal significances can exceed $5σ$ at several benchmark points in the viable parameter space of the Type-X THDM.

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arXiv2025

Probing one-loop--induced decay channel $H^\pm \to W^\pmγ$ in the Two Higgs Doublet Models at muon-TeV colliders

In this work, we study the one-loop--induced decay channel $H^{\pm} \rightarrow W^{\pm}γ$ in the general $\mathcal{R}_ξ$ gauge within Two Higgs Doublet Models. We analytically verify the gauge invariance ($ξ$-independence), ultraviolet finiteness, and renormalization-scale independence of the one-loop form factors, thereby confirming the consistency of our calculations. On the phenomenological side, we perform a parameter scan of the Type-I THDM and, based on the viable parameter space, evaluate the branching ratios of this decay process. Furthermore, we investigate charged Higgs pair production at muon-TeV colliders through the representative processes $μ^+μ^- \rightarrow H^{+}H^{-} \rightarrow W^+W^- hγ$ and $μ^+μ^- \rightarrow γγ\rightarrow H^{+}H^{-} \rightarrow W^+W^- hγ$, as typical applications of our results. The events for the processes are computed within the allowed parameter regions of the Type-I THDM. The corresponding signal significances are evaluated, including the relevant Standard Model backgrounds, at a center-of-mass energy of $\sqrt{s} = 3$~TeV. With the high integrated luminosity expected at muon-TeV colliders, reaching up to $\mathcal{L} = 3000~\text{fb}^{-1}$, our analysis indicates that the signals can be detected with a statistical significance of $5σ$ for several benchmark scenarios in the viable parameter space of the Type-I THDM.

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arXiv2025

When The Standard Model Higgs Meets Its Lighter 95 GeV Twin

Recent reports from the Large Hadron Collider indicate two excesses: one in the lighter Higgs mass region around 95 GeV, and another in the rare $Z γ$ final state of the Standard Model (SM) 125 GeV Higgs decay. These anomalies are analyzed within the minimal gauged two-Higgs-doublet model (G2HDM). A viable parameter space in G2HDM is identified that can account for both excesses. Within the viable parameter space, we find a strong correlation between the signal strengths of the SM 125 GeV Higgs decays into $γγ$ and $Z γ$ modes. However, this correlation does not extend to the lighter 95 GeV Higgs.

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arXiv2025

Processes $γγ\rightarrow ϕ_iϕ_j$ in Inert Higgs Doublet Models and Two Higgs Doublet Models

In this paper, we present a phenomenological analysis of one-loop induced processes $γγ\rightarrow ϕ_iϕ_j$, where the CP-even Higgs bosons are denoted as $ϕ_{i,j} \equiv h,~H$, in high-energy photon-photon collisions, within the frameworks of the Inert Higgs Doublet Model and the Two Higgs Doublet Model. The total cross sections are evaluated as functions of the center-of-mass energy, finding that the cross sections for the considered processes in all the models under investigation are significantly enhanced around the threshold for charged Higgs boson pair production ($\sim 2 M_{H^\pm}$). Furthermore, the enhancement factors, defined as the ratios of cross sections of $γγ\rightarrow ϕ_iϕ_j$ in the investigated models to those for $γγ\rightarrow hh$ in the Standard Model, are examined in the relevant regions of the model's parameter space. In the Inert Higgs Doublet Model, the factors are studied in the parameter space of $(M_{H^\pm},~μ^2_2)$ and $(M_{H^\pm},~λ_2)$. In the Two Higgs Doublet Model, the factors are examined in the planes defined by $(M_{H^\pm},~t_β)$ as well as in the space of the charged Higgs mass $M_{H^\pm}$ and the soft-breaking $Z_2$ parameter $m_{12}^2$. Two scenarios characterized by $c_{β-α} > 0$ and $c_{β-α} < 0$ are studied in further detail. The factors exhibit distinct behaviors between these two scenarios. As a result, it is possible to discriminate between them at future colliders. The dependence of the cross section for the process $γγ\rightarrow hH$ on $m_{12}^2$ provides a potential probe of the soft $Z_2$-breaking scale in the Two Higgs Doublet Model.

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arXiv2025

General Formulas for Loop-Induced Decays of $A \to Zγγ$ and Their Applications

Within the framework of the Standard Model Higgs extensions, including the Two-Higgs-Doublet Model with vector-like fermions and the Triplet-Higgs Model, we derive general one-loop contributions to the rare decay process $A \rightarrow Z γγ$. The analytical expressions are formulated with Passarino-Veltman scalar functions, which represent the scalar coefficients of one-loop Lorentz-covariant tensor integrals. These functions are written in accordance with the input conventions of the {\tt LoopTools} and {\tt Collier} packages, facilitating the efficient numerical generation of decay rates and their distributions using these computational tools. As part of our phenomenological study, we examine the branching ratios of this decay channel within the viable parameter space of the considered models. Our results indicate that the branching ratio can reach $\mathcal{O}(10^{-4})$ in the Two-Higgs-Doublet Model and $\mathcal{O}(10^{-2})$ in the Triplet-Higgs Model at specific points within the allowed parameter regions. Furthermore, the inclusion of vector-like fermions in the loop leads to a significant modification of the partial decay rates, with an observed variation of approximately $10\%$. Additionally, we explore the dependence of the branching ratios on key model parameters, including the charged Higgs mass, mixing angles, and the soft-breaking scale, providing deeper insights into the phenomenological implications of these Higgs-extended frameworks.

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arXiv2025

One-loop induced contributions to the rare decay of $A_0 \rightarrow h_0h_0γ$ in Two Higgs Doublet Models

The analytic expressions for one-loop contributions to the rare decay process $A_0 \rightarrow h_0h_0γ$ within the CP-conserving of Two Higgs Doublet Models are first reported in this paper. Analytic results are presented in term of scalar one-loop Passarino-Veltman functions following the standard output of the packages~{\tt LoopTools} and {\tt Collier}. In this context, physical results for the computed process are easily generated by using one of these packages. The numerical checks are proposed to verify for the analytic results in this paper. The checks rely on the renormalization conditions that the decay amplitude must be the ultraviolet finiteness and infrared finiteness. The amplitude consisting of an external photon always obeys the Ward identity. This will be confirmed numerically in this article. In phenomenological results, the decay rates of $A_0 \rightarrow h_0h_0γ$ are evaluated at several points in the allowed regions of the parameter space. Furthermore, the differential decay widths with respect to the invariant mass of Higgs-pair in final states are studied.

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arXiv2024

$(g-2)_{e,μ}$ and Lepton flavor violating decays in a left-right model

General expressions for one-loop contributions associated with lepton-flavor violating decays of the standard model-like Higgs boson $h\to e_b^\pm e_a^\mp$ and gauge boson $Z\to e^\pm_b e_a^\mp$ are introduced in the unitary gauge. The results are used to discuss these decays as new physics signals in a minimal left-right symmetric model containing only one bidoublet Higgs and a $SU(2)_R$ Higgs doublet accommodating data of neutrino oscillations and $(g-2)_μ$. The numerical investigation indicates that some of these decay rates can reach near future experimental sensitivities.

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arXiv2024

Decay of CP-even Higgs $H\rightarrow h γγ$ in Two Higgs Doublet Model: one-loop analytic results, ward identity checks

The first analytic expressions for loop-induced contributions for the decay of CP-even Higgs $H\rightarrow h γγ$ with $h$ being Standard-Model-like Higgs boson within the framework of Two Higgs Doublet Model are presented in this paper. The one-loop form factors for the decay processes are written in terms of the scalar one-loop Passarino-Veltman functions following the notations of the packages~{\tt LoopTools} and {\tt Collier}. Subsequently, physical results for the decay processes can be generated numerically by using one of the above-mentioned packages. The analytic expressions shown in this paper are verified by several numerical checks, for examples, the ultraviolet and infrared finiteness of one-loop amplitude. Furthermore, the amplitude satisfies the Ward-Takahashi identity due to on-shell photons in final states. The identity is also verified numerically in this work. In phenomenological studies, the differential decay rates as functions of the invariant mass of two photons in final states of $H\rightarrow h γγ$ are first studied in parameter space of the Two Higgs Doublet Models.

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arXiv2024

One-loop analytical expressions for $γγ\rightarrow ϕ_iϕ_j$ in Higgs Extensions of the Standard Models and its applications

General one-loop formulas for loop-induced processes $γγ\rightarrow ϕ_iϕ_j$ with $ϕ_iϕ_j = hh,~hH,~HH$ are presented in the paper. Analytic expressions evaluated in this work are valid for a class of Higgs Extensions of the Standard Models, e.g. Inert Doublet Higgs Models, Two Higgs Doublet Models, Zee-Babu Models as well as Triplet Higgs Models, etc. Analytic expressions for one-loop form factors are written in terms of the basic scalar one-loop two-, three- and four-point functions following the output format of both the packages~{\tt LoopTools} and {\tt Collier}. Physical results can be hence evaluated numerically by using one of the mentioned packages. Analytic results are tested by several checks such as the ultraviolet finiteness, infrared finiteness of the one-loop amplitudes. Furthermore, the amplitudes also obey the ward identity due to the on-shell initial photons. This identity is also verified numerically in this works. In the applications, we present the phenomenological results for Zee-Babu model as a typical example in this report. Production cross-section for the processes $γγ\rightarrow hh$ are scanned over the parameter space of the Zee-Babu Models.

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arXiv2024

One-loop contributions for $A^0 \rightarrow \ell \bar{\ell} V$ with $\ell \equiv e, μ$ and $V\equiv γ, Z$ in Higgs Extensions of the Standard Model

We present one-loop formulas for the decay of CP-odd Higgs $A^0 \rightarrow \ell \bar{\ell} V$ with $\ell \equiv e, μ$ and $V\equiv γ, Z$ in Higgs Extensions of the Standard Model, considering two higgs doublet model with a complex (and real) scalar, two higgs doublet model as well as triplet higgs model. Analytic results for one-loop amplitudes are expressed in terms of Passarino-Veltman functions following the standard notations of {\tt LoopTools}. As a result, physical results can be generated numerically by using the package. In phenomenological results, the total decay widths and the differential decay rates with respect to the invariant mass of lepton pair are analyzed for two typical models such as two higgs doublet model and triplet higgs model.

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arXiv2024

One-loop contributions for $h\rightarrow \ell \bar{\ell}γ$ and $e^-e^+\rightarrow hγ$ in $U(1)_{B-L}$ extension of the standard model

We present one-loop contributing for $h\rightarrow \ell \bar{\ell}γ$ with $\ell =ν_{e,μ, τ}, e, μ$ and $e^-e^+\rightarrow hγ$ in $U(1)_{B-L}$ extension of the standard models. In phenomenological results, the signal strengths for $h\rightarrow \ell \bar{\ell}γ$ at Large Hadron Collider and for $e^-e^+\rightarrow hγ$ at future Lepton Colliders are analyzed in physical parameter space for both vector and chiral $B-L$ models. We find that the contributions from neutral gauge boson $Z'$ to the signal strengths are rather small. Consequently, the effects are hard to probe at future colliders. While the impacts of charged Higgs, CP-odd Higgs in the chiral $B-L$ model on the signal strengths are significant and can be measured with the help of the initial polarization beams at future lepton colliders.

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arXiv2023

One-loop off-shell decay $H^* \rightarrow ZZ$ at future colliders

We present one-loop formulas for contributing to the $HZZ$ vertex in 't Hooft-Veltman gauge within Standard Model framework. One-loop off-shell Higgs decay rates to $Z$-pair are investigated in both unpolarized and longitudinal polarization for $Z$ bosons in final state. The corrections are range of $7\%$ to $8.4\%$ when we vary the off-shell Higgs mass from $200$ GeV to $500$ GeV. In applications, we study off-shell Higgs decay $H^* \rightarrow ZZ$ in the Higgs productions at future colliders such as the signal processes $γ^*(Q^2)γ\rightarrow H^* \rightarrow ZZ$ and $e^-γ\rightarrow e^-H^* \rightarrow e^- ZZ$ are analyzed.

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arXiv2023

One-loop formulas for off-shell decay $H^* \rightarrow W^+W^-$ in 't Hooft-Veltman gauge and its applications

We present analytic results for one-loop radiative corrections to off-shell decay $H^* \rightarrow W^+W^-$ in 't Hooft-Veltman gauge within Standard Model framework. In numerical results, we show off-shell decay rate and its corrections with varying off-shell Higgs mass. The results show that the corrections are of $10\%$ contributions to total decay rates. Furthermore, we study the impacts of one-loop radiative corrections to off-shell decay $H^* \rightarrow W^+W^-$ in Higgs processes at future colliders. The signal processes such as $e^-e^+\rightarrow ZH^*\rightarrow Z(WW)$ with including the initial beam polarizations and $e^-e^+\rightarrow ν_e\barν_e H^* \rightarrow ν_e\barν_e (WW)$ and $e^-γ\rightarrow e^-H^* \rightarrow e^-WW$ are examined. We find that the effects are visible impacts and these should be taken into account at future colliders.

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arXiv2023

One-loop expressions for $h\rightarrow l\bar{l}γ$ in Higgs extensions of the Standard Model

A systematic study of one-loop contributions to the decay channels $h\rightarrow l\bar{l}γ$ with $l=ν_{e,μ, τ}, e, μ$, performed in Higgs extended versions of the Standard Model, is presented in the 't Hooft-Veltman gauge. Analytic formulas for one-loop form factors are expressed in terms of the logarithm and di-logarithmic functions. As a result, these form factors can be reduced to those relating to the loop-induced decay processes $h\rightarrow γγ, Zγ$, confirming not only previous results using different approaches but also close relations between the three kinds of the loop-induced Higgs decay rates. For phenomenological study, we focus on the two observables, namely the enhancement factors defined as ratios of the decay rates calculated between the Higgs extended versions and the standard model, and the forward-backward asymmetries of fermions, which can be used to search for Higgs extensions of the SM. We show that direct effects of mixing between neutral Higgs bosons and indirect contributions of charged Higg boson exchanges can be probed at future colliders.

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