arXiv subjects

S. W. Ham

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

At least 19 recordsLinked to original sources

arXiv2010

Electroweak baryogenesis in the MSSM with vector-like quarks

In the minimal supersymmetric standard model (MSSM), a strongly first-order electroweak phase transition (EWPT) is only possible in a confined parameter region where one of the scalar top quarks is lighter than the top quark and the other one is as heavy as the SUSY breaking scale. If the MSSM is enlarged to accommodate vector-like quarks and their superpartners, we find that the strongly first-order EWPT is possible without requiring light scalar top quark at the one-loop level, in the limit where the lightest scalar Higgs boson of the MSSM behaves like the Higgs boson of the standard model and the other Higgs bosons are all as heavy as the SUSY breaking scale. The strength of the first-order EWPT is found to be dependent on the mass of the lightest neutral Higgs boson and the mixing effects of the vector-like scalar quarks.

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arXiv2010

Higgs boson masses in an extension of the MSSM with vector-like quarks

We study the Higgs sector of the minimal supersymmetric standard model extended with vector-like quarks, at the one-loop level. The radiative corrections to the tree-level masses of the scalar Higgs bosons are calculated by including the contributions from the loops of top quark, vector-like quarks, and their scalar superpartners, for a reasonable parameter region. We find that the mass of the lightest scalar Higgs boson at the one-loop level should be larger than 85 GeV, if we take into account the negative experimental result for the Higgs search at LEP2. As the radiative corrections are calculated in some detail, we also find that the mass of the lightest scalar Higgs boson at the one-loop level is bounded from above at 280 GeV, This upper bound is increased from a previous result. It may provide a wider possibility for the future collider experiments to discover the lightest scalar Higgs boson of this model.

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arXiv2010

Electroweak phase transition in an extension of the Standard Model with scalar color octet

In an extension of the Standard Model with a scalar color octet, the possibility of the strongly first-order electroweak phase transition is studied, by examining the finite-temperature effective Higgs potential at the one-loop level. It is found that there are wide regions in the parameter space that allow the strongly first-order electroweak phase transition, where the Higgs boson mass is larger than the experimental lower bound of 115 GeV, and the masses of the scalar color octet is around 200 GeV. The parameter regions may be explored at the LHC with respect to the electroweak phase transition.

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arXiv2010

Exotic quark effects on the Higgs sector of the USSM at the LHC

The Higgs sector of the U(1)-extended supersymmetric model is studied with great detail. We calculate the masses of the Higgs bosons at the one-loop level. We also calculate at the one-loop level the gluon-involving processes for the productions and decays of the scalar Higgs bosons of the model at the energy of the CERN Large Hadron Collider (LHC), where the radiative corrections due to the loops of top, bottom, and exotic quarks and their scalar partners are taken into account. We find that the exotic quark and exotic scalar quarks in the model may manifest themselves at the LHC, since the production of the heaviest scalar Higgs boson via gluon fusion processes is mediated virtually by the loops of exotic quark and exotic scalar quarks, for a reasonable parameter set of the model.

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arXiv2009

Study of Higgs self couplings of a supersymmetric $E_6$ model at the International Linear Collider

We study the Higgs self couplings of a supersymmetric $E_6$ model that has two Higgs doublets and two Higgs singlets. The lightest scalar Higgs boson in the model may be heavier than 112 GeV, at the one-loop level, where the negative results for the Higgs search at the LEP2 experiments are taken into account. The contributions from the top and scalar top quark loops are included in the radiative corrections to the one-loop mass of the lightest scalar Higgs boson, in the effective potential approximation. The effect of the Higgs self couplings may be observed in the production of the lightest scalar Higgs bosons in $e^+e^-$ collisions at the International Linear Collider (ILC) via double Higgs-strahlung process. For the center of mass energy of 500 GeV with the integrated luminosity of 500 fb$^{-1}$ and the efficiency of 20 %, we expect that at least 5 events of the lightest scalar Higgs boson may be produced at the ILC via double Higgs-strahlung process.

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arXiv2009

Explicit CP violation in the Dine-Seiberg-Thomas model

The possibility of explicit CP violation is studied in a supersymmetric model proposed by Dine, Seiberg, and Thomas, with two effective dimension-five operators. The explicit CP violation may be triggered by complex phases in the coefficients for the dimension-five operators in the Higgs potential, and by a complex phase in the scalar top quark masses. Although the scenario of explicit CP violation is found to be inconsistent with the experimental data at LEP2 at the tree level, it may be possible at the one-loop level. For a reasonable parameter space, the masses of the neutral Higgs bosons and their couplings to a pair of $Z$ bosons are consistent with the LEP2 data, at the one-loop level.

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arXiv2009

Possibility of spontaneous CP violation in Higgs physics beyond the minimal supersymmetric standard model

The Dine-Seiberg-Thomas model (DSTM) is the simplest version of the new physics beyond the minimal supersymmetric standard model (MSSM), in the sense that its Higgs sector has just two dimension-five operators, which are obtained from the power series of the energy scale for the new physics in the effective action analysis. We study the possibility of spontaneous CP violation in the Higgs sector of the DSTM, which consists of two Higgs doublets. We find that the CP violation may be triggered spontaneously by a complex phase, obtained as the relative phase between the vacuum expectation values of the two Higgs doublets. At the tree level, for a reasonably established parameter region, the masses of the three neutral Higgs bosons and their corresponding coupling coefficients to a pair of $Z$ bosons in the DSTM are calculated such that the results are inconsistent with the experimental constraint by the LEP data. Thus, the LEP2 data exclude the possibility of spontaneous CP violation in the DSTM at the tree level. On the other hand, we find that, for a wide area in the parameter region, the CP symmetry may be broken spontaneously in the Higgs sector of the DSTM at the one-loop level, where top quark and scalar top quark loops are taken into account. The upper bound on the radiatively corrected mass of the lightest neutral Higgs boson of the DSTM is about 87 GeV, in the spontaneous CP violation scenario. We confirm that the LEP data does not exclude this numerical result.

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arXiv2009

CP Violation in the Neutral Higgs Sector of a Non-minimal Supersymmetric Standard Model with Multiple Higgs Singlets

The possibility of CP violation is studied in the Higgs sector of a supersymmetric standard model with multiple Higgs singlets. The tree-level Lagrangian in this model is assumed to conserve the CP symmetry. We find that CP violation is viable in this model at the one-loop level, in an explicit way, if the radiative corrections from the third generation of quarks and squarks are taken into account. In the presence of explicit CP violation, at the one-loop level, the upper bound on the mass of the lightest neutral Higgs boson and the productions of the neutral Higgs bosons via the Higgsstrahlung process in high-energy $e^+e^-$ collisions are calculated. We find that the upper bound on the mass of the lightest neutral Higgs boson increases as the number of Higgs singlets increases in a regulated manner. The production cross sections of the neutral Higgs bosons also show a reasonable increasing behavior with respect to the number of Higgs singlets.

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arXiv2008

Spontaneous CP violation in the triplet extended supersymmetric standard model

We find that, at the one-loop level, the spontaneous CP violation is possible in a supersymmetric standard model that has an extra chiral Higgs triplet with hypercharge Y=0. At the tree level, this triplet-extended supersymmetric standard model (TESSM) cannot have any reasonable parameter spaces for the spontaneous CP violation, because the experimental constraints on the coupling coefficient of the neutral Higgs boson to a pair of $Z$ bosons exclude them. By contrast, at the one-loop level, we find that there are experimentally allowed parameter regions, where the spontaneous CP violation may take place. The mass of the lightest neutral Higgs boson in the TESSM in this case may be as large as about 100 GeV, by considering the one-loop contribution due to the top quark and squark loops.

hep-ph↗

arXiv2008

Higgs bosons of a supersymmetric $E_6$ model at the Large Hadron Collider

It is found that CP symmetry may be explicitly broken in the Higgs sector of a supersymmetric $E_6$ model with two extra neutral gauge bosons at the one-loop level. The phenomenology of the model, the Higgs sector in particular, is studied for a reasonable parameter space of the model, in the presence of explicit CP violation at the one-loop level. At least one of the neutral Higgs bosons of the model might be produced via the $WW$ fusion process at the Large Hadron Collider.

hep-ph↗

arXiv2008

Neutral Higgs bosons in the MNMSSM with explicit CP violation

Within the framework of the minimal non-minimal supersymmetric standard model (MNMSSM) with tadpole terms, CP violation effects in the Higgs sector are investigated at the one-loop level, where the radiative corrections from the loops of the quark and squarks of the third generation are taken into account. Assuming that the squark masses are not degenerate, the radiative corrections due to the stop and sbottom quarks give rise to CP phases, which trigger the CP violation explicitly in the Higgs sector of the MNMSSM. The masses, the branching ratios for dominant decay channels, and the total decay widths of the five neutral Higgs bosons in the MNMSSM are calculated in the presence of the explicit CP violation. The dependence of these quantities on the CP phases is quite recognizable, for given parameter values.

hep-ph↗

arXiv2008

Neutral scalar Higgs bosons in the USSM at the LHC

We study the possibility of discovering neutral scalar Higgs bosons in the $U(1)'$-extended supersymmetric standard model (USSM) at the CERN Large Hadron Collider (LHC), by examining their productions via the exotic quark loop in the gluon fusion process at leading order. It is possible in some parameter region that the neutral scalar Higgs bosons may have stronger couplings with the exotic quarks than with top quark. In this case, the exotic quarks may contribute more significantly than top quark in productions of the neutral scalar Higgs bosons in the gluon fusion process. We find that there is indeed some parameter region in the USSM that supports our speculations.

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arXiv2008

Higgs bosons of a supersymmetric $U(1)'$ model at the ILC

We study the scalar Higgs sector of the next-to-minimal supersymmetric standard model with an extra U(1), which has two Higgs doublets and a Higgs singlet, in the light leptophobic $Z'$ scenario where the extra neutral gauge boson $Z'$ does not couple to charged leptons. In this model, we find that the sum of the squared coupling coefficients of the three neutral scalar Higgs bosons to $ZZ$, normalized by the corresponding SM coupling coefficient is noticeably smaller than unity, due to the effect of the extra U(1), for a reasonable parameter space of the model, whereas it is unity in the next-to-minimal supersymmetric standard model. Thus, these two models may be distinguished if the coupling coefficients of neutral scalar Higgs bosons to $ZZ$ are measured at the future International Linear Collider by producing them via the Higgs-strahlung, $ZZ$ fusion, and $WW$ fusion processes.

hep-ph↗

arXiv2007

The Higgs search of the MSSM with explicit CP violation at the LHC and ILC

We study the neutral Higgs sector of the minimal supersymmetric standard model (MSSM) with explicit CP violation at the one-loop level. We take into account the one-loop contributions by the top quark, the stop quarks, the bottom quark, the sbottom quarks, the tau lepton, the stau leptons, the $W$ boson, the charged Higgs boson, the charginos, the $Z$ boson, the neutral Higgs bosons, and the neutralinos. The production cross sections of the neutral Higgs boson are calculated to the leading order. The processes in our consideration are divided in two groups: the Higgs-strahlung and gluon fusion processes accessible at the CERN Large Hadron Collider (LHC), and the vector boson fusion and Higgs-strahlung processes accessible at the $e^+e^-$ International Linear Collider (ILC). In particular, we investigate the dependence of these processes on the CP phase arising from the U(1) factor of the gaugino mass in the neutralino mass matrix. We show that the cross sections of these processes vary by the range of 3% $-$ 19 % as the CP phase changes from zero to $π$.

hep-ph↗

arXiv2007

Higgs bosons of the NMSSM with explicit CP violation at the ILC

We study the Higgs sector of the next-to-minimal supersymmetric standard model (NMSSM) with explicit CP violation at the one-loop level, where the radiative corrections due to the quarks and squarks of the third generation are taken into account. We expect that, within a reasonable region of the parameter space of the present model, at least one of five neutral Higgs bosons may be produced at the future $e^+ e^-$ International Linear Collider (ILC) with $\sqrt{s} = 500$ GeV, with cross section larger than 12 fb, 15 fb, and 1.5 fb, respectively, via the Higgs-strahlung process, the $WW$ fusion process, and the $ZZ$ fusion process. We find that the effect of the CP phase in the present model yields significant influences upon the production cross sections of the five neutral Higgs bosons. We also study the decay modes of the five neutral Higgs bosons to find that their decay widths are similarly affected by the CP phase. Some of the decay modes in the present model behave differently from those of the Standard Model.

hep-ph↗

arXiv2007

Electroweak phase transition in MSSM with $U(1)'$ in explicit CP violation scenario

The possibility of a strongly first-order electroweak phase transition is established in the minimal supersymmetric standard model with an extra $U(1)'$, where a nontrivial CP violating phase is introduced in its Higgs sector. We find that there is a wide region in the parameter space of the model that allows the strongly first-order electroweak phase transition. The mass of stop quark need not be smaller than the top quark mass to ensure the first-order electroweak phase transition be strong. The effect of the CP violating phase upon the strength of the phase transition is discovered. The strength of the phase transition is reduced when the size of the CP violation is increased. For a given CP violating phase, we find that the model has a larger mass for the lightest Higgs boson when it has a stronger phase transition.

hep-ph↗

arXiv2007

Electroweak phase transition in the MNMSSM with explicit CP violation

In explicit CP violation scenario of the minimal non-minimal supersymmetric standard model (MNMSSM), the possibility of a strongly first-order electroweak phase transition (EWPT) is investigated at the one-loop level, where the radiative corrections from the loops of the top and stop quarks are taken into account. Assuming that the stop quark masses are not degenerate, the radiative corrections due to the stop quarks give rise to a CP phase, which triggers the scalar-pseudoscalar mixing in the Higgs sector of the MNMSSM. The lighter stop quark need not always to have a small mass in order to ensure the strongly first-order EWPT. In the MNMSSM with explicit CP violation, it is found that the strength of the first-order EWPT depends on several factors, such as the lightest neutral Higgs boson mass and the nontrivial CP phase arising from stop quark masses. The effects of these factors are discussed.

hep-ph↗

arXiv2007

Electroweak phase transitions in the MSSM with an extra $U(1)'$

We investigate the possibility of electroweak phase transition in the minimal supersymmetric standard model (MSSM) with an extra $U(1)'$. This model has two Higgs doublets and a singlet, in addition to a singlet exotic quark superfield. We find that at the one-loop level this model may accommodate the electroweak phase transitions that are strongly first-order in a reasonably large region of the parameter space. In the parameter region where the phase transitions take place, we observe that the lightest scalar Higgs boson has a smaller mass when the strength of the phase transition becomes weaker. Also, the other three heavier neutral Higgs bosons get more large masses when the strength of the phase transition becomes weaker.

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