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Virtual effects of split-SUSY in Higgs productions at linear colliders

Wang, Fei; Wang, Wenyu; Xu, Fuqiang; Yang, Jin Min; Zhang, HuanjunSubjects: Physics >> The Physics of Elementary Particles and Fields

In split supersymmetry, gauginos and higgsinos are the only supersymmetric particles possibly accessible at foreseeable colliders like the CERN Large Hadron Collider (LHC) and the International Linear Collider (ILC). In order to account for the cosmic dark matter measured by WMAP, these gauginos and higgsinos are stringently constrained and could be explored at the colliders through their direct productions and/or virtual effects in some processes. The clean environment and high luminosity of the ILC render the virtual effects at percent level meaningful in unraveling the new physics effects. In this work we assume split supersymmetry and calculate the virtual effects of the WMAP-allowed gauginos and higgsinos in the Higgs productions e(+) e(-) -> Zh and e(+) e(-) ->nu(e)(nu) over bar (e)h through WW fusion at the ILC. We find that the production cross section of e+ e-. Zh can be altered by a few percent in some part of the WMAP-allowed parameter space, while the correction to the WW fusion process e(+) e(-) ->nu(e) (nu) over bar (e)h is below 1%. Such virtual effects are correlated with the cross sections of chargino pair productions and can offer complementary information in probing split supersymmetry at the colliders. |

Subjects: Physics >> The Physics of Elementary Particles and Fields

As discussed recently by Hooper and Tait, the singlino-like dark matter in the Minimal Supersymmetric Standard Model (MSSM) extended by a singlet Higgs superfield can give a perfect explanation for both the relic density and the Pamela result through the Sommerfeld-enhanced annihilation into singlet Higgs bosons (a or h followed by h -> aa) with a being light enough to decay dominantly to muons or electrons. In this work we analyze the parameter space required by such a dark matter explanation and also consider the constraints from the LEP experiments. We find that although the light singlet Higgs bosons have small mixings with the Higgs doublets in the allowed parameter space, their couplings with the SM-like Higgs boson h(SM) (the lightest doublet-dominant Higgs boson) can be enhanced by the soft parameter A(kappa) and, in order to meet the stringent LEP constraints, the h(SM) tends to decay into the singlet Higgs pairs a a or hh instead of b (b) over bar. So the h(SM) produced at the LHC will give a multi-muon signal, h(SM) -> aa -> 4 mu or h(SM) -> hh -> 4a -> 8 mu. |

Subjects: Physics >> The Physics of Elementary Particles and Fields

If the sparticles are relatively heavy (a few TeV) while the Higgs sector is not so heavy (m(A) is not so large), the Higgs boson Yukawa couplings can harbor sizable quantum effects of sparticles and these large residual effects may play a special role in probing supersymmetry at foreseeable colliders. In this work, focusing on the supersymmetric QCD effects in the hb (b) over bar coupling (h is the lightest CP-even Higgs boson), we give a comparative study for the two popular supersymmetric models: the MSSM and NMSSM. While for both models the supersymmetric QCD can leave over large residual quantum effects in hb (b) over bar coupling, the NMSSM can allow for a much broader region of such effects. Since these residual effects can be over 20% for the hb (b) over bar coupling (and thus over 40% for the ratio Br(h -> b (b) over bar)/Br(h -> tau(+)tau(-))), future measurements may unravel the effects of heavy sparticles or even distinguish the two models. (C) 2009 Elsevier B.V. All rights reserved. |

Subjects: Physics >> The Physics of Elementary Particles and Fields

In the next-to-minimal supersymmetric model (NMSSM) a light CP-odd Higgs boson is so far allowed by current experiments, which, together with a large tan beta, may greatly enhance the rare dileptonic decays B -> X(s)l(+)l(-) and B(s)-> l(+)l(-)gamma. We examine these decays paying special attention to the new operator allowed by the light CP-odd Higgs boson. We find that in the parameter space allowed by current experiments like CERN LEP II and b -> s gamma, the branching ratios of these rare decays can be greatly enhanced, and thus the existing experimental data on B -> X(s)mu(+)mu(-) can further stringently constrain the parameter space (especially the region with a superlight CP-odd Higgs boson and large tan beta). In the surviving parameter space we give the predictions for other dileptonic decay branching ratios and also show the results for the forward-backward asymmetry. |

SUSY dark matter in light of CDMS II results: a comparative study for different models

Cao, Junjie; Hikasa, Ken-ichi; Wang, Wenyu; Yang, Jin Min; Yu, Li-XinSubjects: Physics >> The Physics of Elementary Particles and Fields

We perform a comparative study of the neutralino dark matter scattering on nucleon in three popular supersymmetric models: the minimal (MSSM), the next-to-minimal (NMSSM) and the nearly minimal (nMSSM). First, we give the predictions of the elastic cross section by scanning over the parameter space allowed by various direct and indirect constraints, which are from the measurement of the cosmic dark matter relic density, the collider search for Higgs boson and sparticles, the precision electroweak measurements and the muon anomalous magnetic moment. Then we demonstrate the property of the allowed parameter space with/without the new limits from CDMS II. We obtain the following observations: (i) For each model the new CDMS limits can exclude a large part of the parameter space allowed by current collider constraints; (ii) The property of the allowed parameter space is similar for MSSM and NMSSM, but quite different for nMSSM; (iii) For each model the future SuperCDMS can cover most of the allowed parameter space given that all soft breaking parameters are below 1 TeV. |

Light dark matter in NMSSM and implication on Higgs phenomenology

Cao, Junjie; Hikasa, Ken-ichi; Wang, Wenyu; Yang, Jin MinSubjects: Physics >> The Physics of Elementary Particles and Fields

For the experimental search of neutralino dark matter, it is important to know its allowed mass and scattering cross section with the nucleon. In order to figure out how light a neutralino dark matter can be predicted in low energy supersymmetry, we scan over the parameter space of the NMSSM (next-to-minimal supersymmetric model), assuming all the relevant soft mass parameters to be below TeV scale. We find that in the parameter space allowed by current experiments the neutralino dark matter can be as light as a few GeV and its scattering rate off the nucleon can reach the sensitivity of XENON100 and CoGeNT. As a result, a sizable parameter space is excluded by the current XENON100 and CoGeNT data (the plausible CoGeNT dark matter signal can also be explained). The future 6000 kg-days exposure of XENON100 will further explore (but cannot completely cover) the remained parameter space. Moreover, we find that in such a light dark matter scenario a light CP-even or CP-odd Higgs boson must be present to satisfy the measured dark matter relic density. Consequently, the SM-like Higgs boson h(SM) may decay predominantly into a pair of light Higgs bosons or a pair of neutralinos so that the conventional decays like h(SM) -> gamma gamma is much suppressed. (C) 2011 Elsevier B.V. All rights reserved. |

Split-SUSY dark matter in light of direct detection limits

Cao, Junjie; Wang, Wenyu; Yang, Jin MinSubjects: Physics >> The Physics of Elementary Particles and Fields

We examine the present and future XENON limits on the neutralino dark matter in split supersymmetry (split-SUSY). Through a scan over the parameter space under the current constraints from collider experiments and the WMAP measurement of the dark matter relic density, we find that in the allowed parameter space a large part has been excluded by the present XENON100 limits and a further largish part can be covered by the future exposure (6000 kg day). In case of unobservation of dark matter with such an exposure in the future, the lightest neutralino will remain bino-like and its annihilation is mainly through exchanging the SM-like Higgs boson in order to get the required relic density. (C) 2011 Elsevier B.V. All rights reserved. |

Higgs boson mass in NMSSM with right-handed neutrino

Wang, Wenyu; Yang, Jin Min; You, Lin LinSubjects: Physics >> The Physics of Elementary Particles and Fields

In order to have massive neutrinos, the right-handed neutrino/sneutrino superfield (N) need to be introduced in supersymmetry. In the framework of NMSSM (the MSSM with a singlet S) such an extension will dynamically lead to a TeNT-scale Majorana mass for the right-handed neutrino through the S N N coupling when S develops a vev (the free Majorana mass term is forbidden by the assumed Z(3) symmetry). Also, through the couplings S N N and SHuHd the SM-like Higgs boson (a mixture of H-u, H-d and S) can naturally couple with the right-handed neutrino/sneutrino. As a result, the TeV-scale right-handed neutrino/sneutrino may significantly contribute to the Higgs boson mass. Through an explicit calculation, we find that the Higgs boson mass can indeed be sizably altered by the right-handed neutrino/sneutrino. Such new contribution can help to push up the SM-like Higgs boson mass and thus make the NMSSM more natural. |

Singlet extension of the MSSM as a solution to the small cosmological scale anomalies

Wang, Fei; Wang, Wenyu; Yang, Jin Min; Zhou, SihongSubjects: Physics >> The Physics of Elementary Particles and Fields

In this work we show that the general singlet extension of the minimal supersymmetric standard model (MSSM) can naturally provide a self-interacting singlino dark matter to solve the small cosmological scale anomalies (a large Sommerfeld enhancement factor can also be obtained). However, we find that the NMSSM (the singlet extension of the MSSM with Z(3) symmetry) cannot achieve this due to the restricted parameter space. In our analysis we introduce the concept of symmetric and antisymmetric viscosity cross sections to deal with the nonrelativistic Majorana-fermion dark matter scattering. |

Split supersymmetry under GUT and current dark matter constraints

Wang, Fei; Wang, Wenyu; Yang, Jin MinSubjects: Physics >> The Physics of Elementary Particles and Fields

We recalculate the two-loop beta functions for three gauge couplings taking into account all low energy threshold corrections in split supersymmetry(split-SUSY) which assumes a very high scalar mass scale M-S. We find that in split-SUSY with a gaugino mass unification assumption and with a large M-S the gauge coupling unification requires a lower bound on the gaugino mass. Combined with the constraints from the dark matter relic density and direct detection limits, we find that split-SUSY is very restricted and for dark matter mass below 1 TeV the allowed parameter space can be fully covered by XENON-1T(2017). |