arXiv subjects

Khiem Hong Phan

Publications and source records attributed to Khiem Hong Phan.

36 records · Page 2Linked to original sources

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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arXiv2023

One-loop formulas for $H\rightarrow Z ν_l\barν_l$ for $l = e,μ, τ$ in 't Hooft-Veltman gauge

In this paper, we present analytical results for one-loop contributing to the decay processes $H\rightarrow Z ν_l\barν_l$ (for $l = e, μ, τ$). The calculations are performed within the Standard Model framework in 't Hooft-Veltman gauge. One-loop form factors are then written in terms of scalar one-loop functions in the standard notations of {\tt LoopTools}. As a result, one-loop decay rates for the decay channels can be evaluated numerically by using the package. Furthermore, we analyse the signals of $H\rightarrow Z ν_l\barν_l$ via the production processes $e^-e^+ \rightarrow ZH^* \rightarrow Z (H^* \rightarrow Z ν_l\barν_l)$ including the initial beam polarizations at future lepton collider. The Standard Model background such as the processes $e^-e^+ \rightarrow ν_l\barν_l ZZ$ are also examined in this study. In numerical results, we find that one-loop corrections are about $10\%$ contributions to the decay rates. They are sizeable contributions and should be taken into account at future colliders. We show that the signals $H\rightarrow Zν_l\barν_l$ are clearly visible at center-of-mass energy $\sqrt{s}=250$ GeV and it is hard to probe at higher-energy regions due to the dominant of the background.

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arXiv2022

One-loop on-shell and off-shell decay $H^*\rightarrow VV$ at future $e^-e^-$ collider

One-loop on-shell and off-shell decays $H\rightarrow VV$ with $VV=γγ, Zγ, ZZ$ are presented in this paper. The effects of one-loop on-shell and off-shell Higgs decays in Higgs productions at $e^-e^-$ collisions are also then examined. We find that the impacts of one-loop Higgs decays are significant and they are must be taken into account at $e^-e^-$ collision.

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arXiv2022

One-loop calculations for $H\rightarrow f\bar{f}γ$ in the $U(1)_{B-L}$ extension for Standard Model

In this paper, we present the calculations for $H\rightarrow f\bar{f}γ$ in the $U(1)_{B-L}$ extension for Standard Model. Analytic results for one-loop form factors in the decay process are expressed in terms of the scalar one-loop Passarino$-$Veltman functions in the conventions of {\tt LoopTools}. Therefore, the decay rates can be evaluated numerically by using this package. In phenomenological results, we show the differential decay rates with respect to invariant mass of fermion pair $m_{ff}$, new neutral gauge mass $M_{Z'}$ and the coupling $g'$ of $U(1)_{B-L}$ gauge group. We find that the contributions of the $U(1)_{B-L}$ extension for Standard Model are visible effects and they must be taken into account at future colliders.

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arXiv2022

An explanation of experimental data of $(g-2)_{e,μ}$ in 3-3-1 models with inverse seesaw neutrinos

We show that the anomalous magnetic moment experimental data of muon and electron $(g-2)_{μ,e}$ can be explained simultaneously in simple extensions of the 3-3-1 models consisting of new heavy neutrinos and a singly charged Higgs boson. The heavy neutrinos generate active neutrino masses and mixing through the general seesaw mechanism. They also have non-zero Yukawa couplings with singly charged Higgs bosons and right-handed charged leptons, which result in large one-loop contributions known as \emph{chirally-enhanced} ones. Numerical investigation confirms a conclusion indicated previously that these contributions are the key point to explain the large $(g-2)_{μ,e}$ data, provided that the inverse seesaw mechanism is necessary to allow both conditions that heavy neutrino masses are above few hundred GeV and non-unitary part of the active neutrino mixing matrix must be large enough.

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arXiv2021

One-loop contributions to the decay $H\rightarrow ν_l\barν_lγ$ in standard model revisited

One-loop contributions to the decay $H\rightarrow ν_l\barν_lγ$ with $l=e, μ, τ$ within standard model framework are revisited in this paper. We derive two representations for the form factors in this calculation. As a result, the computations are not only checked numerically by verifying the ultraviolet finiteness of the results but also confirming the ward identity of the amplitude. We find that the results are good stability with varying ultraviolet cutoff parameters as well as satisfy the ward identity. In phenomenological results, all the physical results are examined with the present input parameters. Especially, we study the partial decay widths for the decay channels in both cases of the detected photon and invisible photon. Differential decay widths are also generated as a function of energy of final photon.

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arXiv2021

General one-loop formulas for $H\rightarrow f\bar{f}γ$ and its applications

We present general one-loop contributions to the decay processes $H\rightarrow f\bar{f}γ$ including all possible the exchange of the additional heavy vector gauge bosons, heavy fermions, and charged (also neutral) scalar particles in the loop diagrams. As a result, the analytic results are valid in a wide class of beyond the standard models. Analytic formulas for the form factors are expressed in terms of Passarino-Veltman functions in the standard notations of {\tt LoopTools}. Hence, the decay rates can be computed numerically by using this package. The computations are then applied to the cases of the standard model, $U(1)_{B-L}$ extension of the standard model as well as two Higgs doublet model. Phenomenological results of the decay processes for all the above models are studied. We observe that the effects of new physics are sizable contributions and these can be probed at future colliders.

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arXiv2021

One-loop $W$ boson contributions to the decay $H\rightarrow Zγ$ in the general $R_ξ$ gauge

One-loop $W$ boson contributions to the decay $H\rightarrow Zγ$ in the general $R_ξ$ gauge are presented. The analytical results are expressed in terms of well-known Passarino-Veltman functions which their numerical evaluations can be generated using {\tt LoopTools}. In the limit $d\rightarrow 4$, we have shown that these analytical results are independent of the unphysical parameter $ξ$ and consistent with previous results. The gauge parameter independence are also checked numerically for consistence. Our results are also well stable with different values of $ξ=0, 1, 100,$ and $ξ\rightarrow \infty$.

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arXiv2021

General one-loop contributions to the decay $H\rightarrow ν_l\barν_lγ$

General one-loop contributions to the decay amplitudes $H\rightarrow ν_l\barν_lγ$ are presented, considering all possible contributions of additional heavy vector gauge bosons, fermions, and charged (and also neutral) scalar particles appearing in the loop diagrams. Moreover, the results can be applied directly when extra neutrinos (apart from three ones in standard model) are taken into account in final states. Analytic results are presented in terms of Passarino-Veltman scalar functions which can be evaluated numerically using {\tt LoopTools}. In the standard model framework, these analytical results are generated and cross-checked with previous computations. We find that our results are well consistent with these computations. Within standard model limit, phenomenological results for the decay channels are also studied using the updated input parameters at the Large Hadron Collider.

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arXiv2021

One-loop form factors for $H\rightarrow γ^γ^$ in $R_ξ$ gauge

In this paper, we present general one-loop form factors for $H\rightarrow γ^* γ^*$ in $R_ξ$ gauge, considering all cases of two on-shell, one on-shell and two off-shell for final photons. The calculations are performed in standard model and in arbitrary beyond the standard models which charged scalar particles may be exchanged in one-loop diagrams. Analytic results for the form factors are shown in general forms which are expressed in terms of the Passarino-Veltman functions. We also confirm the results in previous computations which are available for the case of two on-shell photons. The $ξ$-independent of the result is also discussed. We find that numerical results are good stability with varying $ξ=0,1$ and $ξ\rightarrow \infty$.

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arXiv2020

Scalar 1-loop Feynman integrals as meromorphic functions in space-time dimension d, II: Special kinematics

Based on the method developed in [K.~H.~Phan and T.~Riemann, Phys.\ Lett.\ B {\bf 791} (2019) 257], detailed analytic results for scalar one-loop two-, three-, four-point integrals in general $d$-dimension are presented in this paper. The calculations are considered all external kinematic configurations and internal mass assignments. Analytic formulas are expressed in terms of generalized hypergeometric series such as Gauss $_2F_1$, Appell $F_1$ and Lauricella $F_S$ functions.

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arXiv2020

Hypergeometric presentation for one-loop contributing to $H\rightarrow Zγ$

In this paper, new analytic formulas for one-loop contributing to Higgs decay channel $H \rightarrow Zγ$ are presented in terms of hypergeometric functions. The calculations are performed by following the technique for tensor one-loop reduction developed in [A.~I.~Davydychev, Phys.\ Lett.\ B {\bf 263} (1991) 107]. For the first time, one-loop form factors for the decay process are shown which are valid at arbitrary space-time dimension $d$.

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arXiv2019

One-loop three-point Feynman integrals with Appell $F_1$ hypergeometric functions

New analytic formulas for one-loop three-point Feynman integrals in general space-time dimension ($d$) are presented in this paper. The calculations are performed at general configurations for internal masses and external momenta. The analytic results are expressed in terms of hypergeometric series $_2F_1$, $_3F_2$ for special cases and Appell $F_1$ for general cases. Furthermore, we cross-check our analytic results with other references which have carried out the integrals in several special cases.

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arXiv2018

Scalar 1-loop Feynman integrals as meromorphic functions in space-time dimension d

The long-standing problem of representing the general massive one-loop Feynman integral as a meromorphic function of the space-time dimension $d$ has been solved for the basis of scalar one- to four-point functions with indices one. In 2003 the solution of difference equations in the space-time dimension allowed to determine the necessary classes of special functions: self-energies need ordinary logarithms and Gauss hypergeometric functions $_2F_1$, vertices need additionally Kampé de Fériet-Appell functions $F_1$, and box integrals also Lauricella-Saran functions $F_S$. In this study, alternative recursive Mellin-Barnes representations are used for the representation of $n$-point functions in terms of $(n-1)$-point functions. The approach enabled the first derivation of explicit solutions for the Feynman integrals at arbitrary kinematics. In this article, we scetch our new representations for the general massive vertex and box Feynman integrals and derive a numerical approach for the necessary Appell functions $F_1$ and Saran functions $F_S$ at arbitrary kinematical arguments.

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arXiv2017

Scalar one-loop vertex integrals as meromorphic functions of space-time dimension d

Representations are derived for the basic scalar one-loop vertex Feynman integrals as meromorphic functions of the space-time dimension $d$ in terms of (generalized) hypergeometric functions $_2F_1$ and $F_1$. Values at asymptotic or exceptional kinematic points as well as expansions around the singular points at $d=4+2n$, $n$ non-negative integers, may be derived from the representations easily. The Feynman integrals studied here may be used as building blocks for the calculation of one-loop and higher-loop scalar and tensor amplitudes. From the recursion relation presented, higher n-point functions may be obtained in a straightforward manner.

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arXiv2017

A new method for evaluating scalar one-loop Feynman integrals in general space-time dimension

In this paper, we propose a new method for evaluating scalar one-loop Feynman integrals in generalized D-dimension. The calculations play an important building block for two-loop and higher-loop corrections to the processes at future colliders such as the Large Hadron Collider (LHC) and the International Linear Collider (ILC). In this method, scalar one-loop N-point functions will be presented as the one-fold Mellin-Barnes representation of (N-1)-point ones with shifting space-time dimension. This representation offers a clear advantage that we can construct recursively the analytic expressions for N-point functions from the basic ones which are one-point functions. The compact formulae for scalar one-loop two-point functions with massive internal lines and three-point, four-point functions with massless internal lines are given as examples in this article. In particular, they are written in terms of generalized hypergeometric series such as Gauss, Appell F 1 functions. We also perform a sample numerical check for the analytical expressions in this report by comparing with LoopTools and AMBRE/MB. We find that the numerical results from this work are in good agreement with LoopTools at $ε^0$ -expansion and AMBRE/MB at higher-order of $ε$-expansion, at higher D-dimension.

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arXiv2015

General $\varepsilon$-representation for scalar one-loop Feynman integrals

A systematic study of the scalar one-loop two-, three-, and four-point Feynman integrals is performed. We consider all cases of mass assignment and external invariants and derive closed expressions in arbitrary space-time dimension in terms of higher transcendental functions. The integrals play a role as building blocks in general higher-loop or multi-leg processes. We also perform numerical checks of the calculations using AMBRE/MB and LoopTools/FF.

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arXiv2014

Thermodynamics for Trajectories of a Mass Point

On the basis of information theory, a new formalism of classical non-relativistic mechanics of a mass point is proposed. The particle trajectories of a general dynamical system defined on an (1+n)-dimensional smooth manifold are treated geometrically as dynamical variables. Statistical mechanics of particle trajectories are constructed in a classical manner. Thermodynamic variables are introduced through a partition function based on a canonical ensemble of trajectories. Within this theoretical framework, classical mechanics can be interpreted as an equilibrium state of statistical mechanics. The relationships between classical and quantum mechanics are discussed from this statistical mechanical viewpoint. The maximum entropy principle is shown to provide a unified view of both classical and quantum mechanics.

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