arXiv subjects

S. W. Ham

Publications and source records attributed to S. W. Ham.

33 records · Page 2Linked to original sources

arXiv2007

Explicit CP violation in a MSSM with an extra $U(1)'$

We study that a minimal supersymmetric standard model with an extra $U(1)'$ gauge symmetry may accommodate the explicit CP violation at the one-loop level through radiative corrections. This model is CP conserving at the tree level and cannot realize the spontaneous CP violation for a wide parameter space at the one-loop level. In explicit CP violation scenario, we calculate the Higgs boson masses and the magnitude of the scalar-pseudoscalar mixings in this model at the one-loop level by taking into account the contributions of top quarks, bottom quarks, exotic quarks, and their superpartners. In particular, we investigate how the exotic quarks and squarks would affect the scalar-pseudoscalar mixings. It is observed that the size of the mixing between the heaviest scalar and pseudoscalar Higgs bosons is changed up to 20 % by a complex phase originated from the exotic quark sector of this model.

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arXiv2007

Phase transition in a supersymmetric axion model

In a supersymmetric axion model where the scale for both supersymmetry breaking and Peccei-Quinn symmetry breaking is around $10^{11}$ GeV, we find that there is a reasonable parameter space for a strongly first order phase transition at the scale.

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arXiv2005

Electroweak phase transition in an extension of the standard model with a real Higgs singlet

The Higgs potential of the standard model with an additional real Higgs singlet is studied in order to examine if it may allow the strongly first order electroweak phase transition. It is found that there are parameter values for which this model at the one-loop level with finite temperature effect may allow the desired phase transition. Those parameter values also predict that the masses of the neutral scalar Higgs bosons of the model are consistent with the present experimental bound, and that their productions in $e^+e^-$ collisions may be searched at the proposed ILC with $\sqrt s$ = 500 GeV in the near future.

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arXiv2005

Electroweak phase transition and Higgs self-couplings in the two-Higgs-doublet model

We calculate both the cubic and the quartic self-couplings of the lighter scalar Higgs boson without assuming the decoupling limit in the two-Higgs-doublet model (THDM). In some regions of parameter space of the THDM where the electroweak phase transition is strongly first order, it is possible that the quartic self-coupling of the lighter scalar Higgs boson might be deviated by at least 40 % from the standard model prediction.

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arXiv2004

Electroweak phase transition in the MSSM with four generations

By assuming the existence of the sequential fourth generation to the minimal supersymmetric standard model (MSSM), we study the possibility of a strongly first-order electroweak phase transition. We find that there is a parameter region of the MSSM where the electroweak phase transition is strongly first order. In that parameter region, the mass of the lighter scalar Higgs boson is calculated to be above the experimental lower bound, and the scalar quarks of the third and the fourth generations are heavier than the corresponding quarks.

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arXiv2004

Electroweak phase transition in the standard model with a dimension-six Higgs operator at one-loop level

The possibility of a strongly first-order electroweak phase transition by means of a dimension-six Higgs operator in the Higgs potential of the standard model is studied at finite temperature at the one-loop level. Exact calculation of the one-loop effective Higgs potential at finite temperature suggests that for the Higgs boson with its mass between 115 and 132 GeV the strongly first-order electroweak phase transition is possible if a dimension-six operator is present.

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arXiv2004

Electroweak phase transition in a nonminimal supersymmetric model

The Higgs potential of the minimal nonminimal supersymmetric standard model (MNMSSM) is investigated within the context of electroweak phase transition. We investigate the allowed parameter space yielding correct electroweak phase transitoin employing a high temperature approximation. We devote to phenomenological consequences for the Higgs sector of the MNMSSM for electron-positron colliders. It is observed that a future $e^+ e^-$ linear collider with $\sqrt{s} = 1000$ GeV will be able to test the model with regard to electroweak baryogenesis.

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arXiv2003

Radiative CP violation in the Higgs sector of the Next-to-minimal supersymmetric model

We investigate the neutral Higgs sector in the next-to-minimal supersymmetric standard model (NMSSM) with explicit CP violation at the one-loop level by using the effective potential method. In general, explicit CP violation is possible at the tree-level in the Higgs potential of the NMSSM, which may possess a complex phase. The tree-level Higgs potential can be made CP conserving by assuming that all the relevant parameters are real. However, the CP-conserving Higgs potential at the tree level may still develop complex phases at the one-loop level through radiative corrections. These complex phases exhibit explicit CP violation through the mixings between the scalar and pseudoscalar Higgs bosons. One of the complex phases arise in the neutralino sector. For a particular choice of the relevant parameter values, the scalar-pseudoscalar mixings are found to strongly dependent on this phase. Meanwhile, for a wide region in the parameter space, the ratios of CP mixing elements of the neutral Higgs boson mass matrix to CP non-mixing ones increase weakly against this phase. Also, the neutral Higgs boson masses are roughly stable against the variation of this phase.

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arXiv2003

The neutral Higgs boson masses of MSSM at one-loop level in explicit CP violation scenario

The neutral Higgs sector of the minimal supersymmetric standard model (MSSM) in explicit CP violation scenario is investigated at the one-loop level. Within the context of the effective potential formalism, the masses of the neutral Higgs bosons are calculated at the one-loop level by taking into account the contributions of the following loops of ordinary particles and superpartners: top quark, the scalar top quarks, bottom quark, the scalar bottom quarks, tau lepton, the scalar tau leptons, $W$ boson, the charged Higgs boson, the charginos, $Z$ boson, the scalar and pseudoscalar Higgs bosons, and the neutralinos. Our calculation is an improvement in the sense that both the terms which are quartic in the electroweak coupling constants into account, and the pseudoscalar Higgs loop contribution are explicitly included.

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arXiv2002

Possibility of spontaneous CP violation in the nonminimal supersymmetric standard model with two neutral Higgs singlets

A supersymmetric standard model with two Higgs doublets and two Higgs singlets is investigated if it can accommodate the possibility of spontaneous CP violation. Assuming the degeneracy of the scalar quark masses of the third generation, we find that spontaneous CP violation in the Higgs sector is viable in our model. In the case of spontaneous CP violation, the masses of the lightest two neutral Higgs bosons are estimated to be 80 and 125 GeV for some parameter values in our model, which, are consistent with LEP2 data.

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arXiv2002

Charged Higgs boson in the next-to-minimal supersymmetric standard model with explicit CP violation

The phenomenology of the explicit CP violation in the Higgs sector of the next-to-minimal supersymmetric standard model (NMSSM) is investigated, with emphasis on the charged Higgs boson. The radiative corrections due to both quarks and scalar-quarks of the third generation are taken into account, and the negative result of the search for the Higgs bosons at CERN LEP2, with the discovery limit of 0.1 pb, is imposed as a constraint. It is found that there are parameter regions of the NMSSM where the lightest neutral Higgs boson may even be massless, without being detected at LEP2. This implies that the LEP2 data do not contradict the existence of a massless neutral Higgs boson in the NMSSM. For the charged Higgs boson, the radiative corrections to its mass may be negative in some parameter regions of the NMSSM. The phenomenological lower bound on the radiatively corrected mass of the charged Higgs boson is increased as the CP violation becomes maximal, i.e., as the CP violating phase becomes $π/2$. At the maximal CP violation, its lower bound is about 110 GeV for 5 $\leqslant \tan β\leqslant$ 40. The vacuum expectation value (VEV) of the neutral Higgs singlet is shown to be no smaller than 16 GeV for any parameter values of the NMSSM with explicit CP violation. This value of the lower limit is found to increase up to about 45 GeV as the ratio ($\tan β$) of the VEVs of the two Higgs doublets decreases to smaller values ($\sim$ 2). The discovery limit of the Higgs boson search at LEP2 is found to cover about a half of the kinematically allowed part of the whole parameter space of the NMSSM, and the portion is roughly stable against the CP violating phase.

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arXiv2002

Neutral Higgs sector of the next-to-minimal supersymmetric standard model with explicit CP violation

The neutral Higgs sector of the next-to-minimal supersymmetric standard model (NMSSM) with explicit CP violation is investigated at the 1-loop level, using the effective potential method; not only the loops involving the third generation of quarks and scalar quarks, but also the loops involving $W$ boson, charged Higgs boson, and chargino are taken into account. It is found that for some parameter values of the NMSSM the contributions from the $W$ boson, charged Higgs boson, and chargino loops may modify the masses of the neutral Higgs bosons and the mixings among them significantly, depending on the CP phase. In $e^+e^-$ collisions, the prospects for discovering neutral Higgs bosons are investigated within the context of the NMSSM with explicit CP violation when the dominant component of the lightest neutral Higgs boson is the Higgs singlet field of the NMSSM.

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arXiv1999

Spontaneous Violation of the CP Symmetry in the Higgs Sector of the Next-to-Minimal Supersymmetric Model

The spontaneous violation of the CP symmetry in the next-to-minimal supersymmetric standard Model (NMSSM) is investigated. It is found that the spontaneous violation of the CP symmetry can occur in the Higgs sector of the NMSSM for a wide region of the parameter space of the model, at the 1-loop level where the radiative corrections due to the top quark and scalar-top quark loops are found to generate the scalar-pseudoscalar mixings between the two Higgs doublets of the NMSSM. In our model, we assume that the masses of the left-handed and the right-handed scalar-top quarks are not degenerate. And we investigate our model anaytically: We derive analytical formulae of the 1-loop mass matrix for the neutral Higgs bosons. We calculate the upper bound on the lightest neutral Higgs boson mass under the assumption. It is found to be about 140 GeV for our choice of parameter values in the presence of the spontaneous violation of the CP symmetry in the NMSSM. Thus, the possibility of the spontaneous violation of the CP symmetry is not completely ruled out in the Higgs sector of the NMSSM if the masses of the left-handed and the right-handed scalar-top quarks are not degenerate. Further, the phenomenology of the $K$-${\bar K}$ mixing within the context of our model is studied. The lower bound on CP violating phase in the $K$-${\bar K}$ mixing is found to increase if either $\tanβ$ decreases or $A_t$ increases.

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arXiv1996

Production of Nonlinear SUSY Higgs Bosons at $e^+ e^-$ Colliders

We investigate the Higgs sector of a nonlinear supersymmetric standard model at LEP 1 and LEP 2, as well as at future linear $e^+ e^-$ colliders with $\sqrt s = 500$, 1000, and 2000 GeV. The LEP 1 data do not put any constraints on the parameters of the model, and allow a massless Higgs boson in particular. For LEP 2, there are remarkable differences between the Higgs productions at $\sqrt s = 175$ GeV on the one hand and that at $\sqrt s = 192$ GeV and 205 GeV on the other hand. The case for $\sqrt s = 175$ GeV is similar to LEP 2, whereas those for $\sqrt s = 192$ GeV and 205 GeV will be able to give experimental constraints on the parameters. Finally the $e^+ e^-$ colliders with $\sqrt s = 500$, 1000, and 2000 GeV are most probably able to test the model conclusively.

hep-ph↗

arXiv1996

Higgs Physics at LEP2

In this report we review the prospects for Higgs physics at LEP2. The theoretical aspects and the phenomenology of Higgs particles are discussed within the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). The experimental search techniques are described and the discovery limits for Higgs bosons in the LEP2 energy range are summarized. In addition, opportunities of detecting Higgs particles in non-minimal extensions of the SM and the MSSM are investigated.

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