119273290
Revisit to non-decoupling MSSM
Abstract Dipole operator s ¯ σ μ ν F μ ν b requires the helicity flip in the involving quark states thus the breaking of chiral U ( 3 ) Q × U ( 3 ) d . On the other hand, the b quark mass generation is also a consequence of chiral U ( 3 ) Q × U ( 3 ) d symmetry breaking. Therefore, in many models, there might be strong correlation between the b → s γ and b quark Yukawa coupling. In this Letter, we use non-decoupling MSSM model to illustrate this feature. In the scenario, the light Higgs boson may evade the direct search experiments at LEPII or Tevatron while the 125 GeV Higgs-like boson is identified as the heavy Higgs boson in the spectrum. A light charged Higgs is close to the heavy Higgs boson which is of 125 GeV and its contribution to b → s γ requires large supersymmetric correction with large PQ and R -symmetry breaking. The large supersymmetric contribution at the same time significantly modifies the b quark Yukawa coupling. With combined flavor constraints B → X s γ and B s → μ + μ − and direct constraints on Higgs properties, we find best fit scenarios with light stop of O ( 500 GeV ) , negative A t around − 750 GeV and large μ -term of 2–3 TeV. In addition, reduction in b b ¯ partial width may also result in large enhancement of ττ decay branching fraction. Large parameter region in the survival space under all bounds may be further constrained by H → τ τ if no excess of ττ is confirmed at LHC. We only identify a small parameter region with significant H → h h decay that is consistent with all bounds and reduced ττ decay branching fraction. In the end, if current dark matter mostly consists of neutralino, direct detection experiments like XENON100 also puts stringent bound over this scenario with light Higgs bosons. The light stops which are required by flavor constraints can further enhance the scattering cross section.
119216012
Dielectron and diphoton channels in 2HDM
Abstract It was observed recently that [L. Randall, Mark B. Wise, arXiv: 0807.1746 [hep-ph] ], any particle in the Standard Model cannot decay to e + e − and γγ final states with comparably measurable branching ratios. This is also true for most extensions of the Standard Model, with the Randall–Sundrum model as an outstanding exception. In this Letter, we show that two-Higgs-Doublet-Models (2HDM) yield another possible exception if certain parameters are properly chosen. In addition, we have checked that this model survives the tests of low energy processes, including the anomalous magnetic moment and electric dipole moment of leptons, lepton-flavor-violating decays μ − → e − γ and e − e + e − .
119298883
Is polarization effect visible in leptonic SUSY searches?
X iv :1 31 2. 15 27 v1 [ he pph ] 5 D ec 2 01 3 Is polarization effect visible in leptonic SUSY searches? Kai Wang, Liucheng Wang, Tao Xu , and Liangliang Zhang a Zhejiang Institute of Modern Physics and Department of Physics, Zhejiang University, Hangzhou, Zhejiang 310027, CHINA b Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA c School of Physics, Nankai University, Tianjin 300071, CHINA
119224770
Gamma-rays from nearby clusters: Constraints on selected decaying dark matter models
Abstract Recently, the Fermi-LAT Collaboration reported upper limits on the GeV gamma-ray flux from nearby clusters of galaxies. Motivated by these limits, we study corresponding constraints on gamma-ray emissions from two specific decaying dark matter models, one via grand unification scale suppressed operators and the other via R-parity violating operators. Both can account for the PAMELA and Fermi-LAT excesses of e ± . For GUT decaying dark matter, the gamma-rays from the M49 and Fornax clusters, with energy in the range of 1 to 10 GeV, lead to the most stringent constraints to date. As a result, this dark matter is disfavored with conventional model of e ± background. In addition, it is likely that some tension exists between the Fermi-LAT e ± excess and the gamma-ray constraints for any decaying dark matter model, provided conventional model of e ± background is adopted. Nevertheless, the GUT decaying dark matter can still solely account for the PAMELA positron fraction excess without violating the gamma-ray constraints. For the gravitino dark matter model with R-parity violation, cluster observations do not give tight constraints. This is because a different e ± background has been adopted which leads to relatively light dark matter mass around 200 GeV.
119285074
Light top squark in precision top quark sample
The uncertainty of $t\bar{t}$ production cross section measurement at LHC is at a-few-percent level which still allows the stop pair production $\tilde{t}\tilde{t}^{*}$ with identical final states $2b+\ell+nj+{E}_{T}$. In this paper, we attempt to use the existing measurement of $W$-polarization in top quark decay to improve the distinction between stop and top quark states. We apply the ATLAS $\chi^2$ method of $W$-polarization measurement in semi-leptonic $t\bar{t}$ final state to semi-leptonic stop pair samples and study its prediction. We find that the faked top events from stop mostly contribute to the left-handed polarized $W$ due to the reconstruction. The benchmark point with maximal contribution to top events only changes $F_{L}$ by 1%. After comparing with the current experiments, we conclude that the current measurement of $W$-polarization in $t$ decay cannot exclude the light stop scenario.
73712405
Decaying dark matter in supersymmetric SU(5) models
Abstract Motivated by recent observations from PAMELA, Fermi and H.E.S.S., we consider dark matter decays in the framework of supersymmetric SU(5) grand unification theories. An SU(5) singlet S is assumed to be the main component of dark matters, which decays into visible particles through dimension six operators suppressed by the grand unification scale. Under certain conditions, S decays dominantly into a pair of sleptons with universal coupling for all generations. Subsequently, electrons and positrons are produced from cascade decays of these sleptons. These cascade decay chains smooth the e + + e − spectrum, which permit naturally a good fit to the Fermi-LAT data. The observed positron fraction upturn by PAMELA can be reproduced simultaneously. We have also calculated diffuse gamma-ray spectra due to the e ± excesses and compared them with the preliminary Fermi-LAT data from 0.1 GeV to 10 GeV in the region 0 ° ⩽ l ⩽ 360 ° , 10 ° ⩽ | b | ⩽ 20 ° . The photon spectrum of energy above 100 GeV, mainly from final state radiations, may be checked in the near future.
118073401
Observation of $\eta_{c}$ decay into $\Sigma^{+}\bar{\Sigma}^{-}$ and $\Xi^{-}\bar{\Xi}^{+}$ final states
Using a data sample of $2.25\times10^{8}$ $J/\psi$ events collected with the BESIII detector, we present the first observation of the decays of $\eta_{c}$ mesons to $\Sigma^{+}\bar{\Sigma}^{-}$ and $\Xi^{-}\bar{\Xi}^{+}$. The branching fractions are measured to be $(2.11\pm0.28_{\rm stat.}\pm0.18_{\rm syst.}\pm0.50_{\rm PDG})\times10^{-3}$ and $(0.89\pm0.16_{\rm stat.}\pm0.08_{\rm syst.}\pm0.21_{\rm PDG})\times10^{-3}$ for $\eta_{c} \to \Sigma^{+}\bar{\Sigma}^{-}$ and $\Xi^{-}\bar{\Xi}^{+}$, respectively. These branching fractions provide important information on the helicity selection rule in charmonium-decay processes.
119257125
Higgs boson decays and production via gluon fusion at LHC in littlest Higgs models with T-parity
We study the Higgs boson decays and production via gluon fusion at the LHC as a probe of two typical littlest Higgs models which introduce a top quark partner with different (even and odd) T parity to cancel the Higgs mass quadratic divergence contributed by the top quark. For each model, we consider two different choices for the down-type quark Yukawa couplings. We first examine the branching ratios of the Higgs boson decays and then study the production via gluon fusion followed by the decay into two photons or two weak gauge bosons. We find that the predictions can be quite different for different models or different choices of down-type quark Yukawa couplings, and all these predictions can sizably deviate from the standard model predictions. So the Higgs boson processes at the LHC can be a sensitive probe for these littlest Higgs models.
118438822
Dark matter and Higgs phenomenology predicted by left-right twin Higgs model in light of CDMS II results
The left-right twin Higgs model predicts a light stable scalar Ŝ, which is a candidate for WIMP dark matter. We study its scattering on nucleon and find that the cross section is below the CDMS II upper bound but can reach the SuperCDMS sensitivity. Then we study the Higgs phenomenology by paying special attention to the decay h → ŜŜ which is strongly correlated with the dark matter scattering on nucleon. We find that such an invisible decay can be sizable, which can severely suppress the conventional decay modes like h → VV (V = W, Z) and $ h \to b\bar b $. On the other hand, compared to the SM prediction, the rates of Higgs boson productions at the LHC via gluon-gluon fusion, weak boson fusion or in association with top quark pairs are all reduced significantly, e.g., the gluon-gluon fusion channel can be suppressed by about 30%.
125260045
Evidence of sigma particle in J / psi ---> omega pi pi
118951209
Phenomenology and theory of possible light Higgs bosons
We study the implications of the absence of a direct discovery of a Higgs boson at LEP. First we exhibit 15 physically different ways in which one or more Higgs bosons lighter than the LEP limit could still exist. In the minimal supersymmetric standard model (MSSM) all of these, as well as the cases where mh ≥ 115 GeV, seem fine-tuned. We examine some interpretations of the fine tuning in high scale theories. The least fine-tuned MSSM outcome will have mh ≃ 115 GeV, while approaches that extend the MSSM at the weak scale can naturally have larger mh.