分类: 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: Since the top quark FCNC processes are extremely supressed in the Standard Model (SM) but could be greatly enhanced in some new physics models, they could serve as a smoking gun for new physics hunting at the LHC. In this brief review we summarize the new
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: 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.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: 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.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-17
摘要: A supersymmetric model with two copies of the StandardModel gauge groups is constructed in the gauge mediated supersymmetry breaking scenario. The supersymmetry breaking messengers are in a simple form. The Standard Model is obtained after first step gauge symmetry breaking. In the case of one copy of the gauge interactions being strong, a scenario of electroweak symmetry breaking is discussed, and the gauginos are generally predicted to be heavier than the sfermions.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We propose a realistic flipped SU(5) model derived from a five-dimensional orbifold SO(10) model. The Standard Model (SM) fermion masses and mixings are explained by combining the traditional Froggatt-Nielsen mechanism with the five-dimensional wave function profiles of the SM fermions. Employing tree-level spontaneous R-symmetry breaking in the hidden sector and extra( ordinary) gauge mediation, we obtain realistic supersymmetry breaking soft mass terms with non-vanishing gaugino masses. Including the messenger fields at the intermediate scale and Kaluza-Klein states at the compactification scale, we study gauge coupling unification. We show that the SO(10) unified gauge coupling is very strong and the unification scale can be much higher than the compactification scale. We briefly discuss proton decay as well.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-17
摘要: A supersymmetric model with gauge symmetry G1 × G2, where Gi = SU(3)i × SU(2)i × U(1)i, is constructed within the framework of gauge me-diated supersymmetry breaking. At the energy scale ∼ (10−100) TeV wherem the gauge symmetry breaks down to the Standard Model (SM), G1 is strong and G2 is weak. The observed gauge coupling constant unification of the SM is attributed to that of G2. The messenger fields and Higgs fields just sat-isfy the condition that makes G2 a realization of strong unification. The SMgauginos are predicted to be generally heavier than the sleptons and squarks.
分类: 物理学 >> 核物理学 提交时间: 2016-09-10
摘要: A summary of the constraints from the ATLAS experiment on R-parity conserving supersymmetry is presented. Results from 22 separate ATLAS searches are considered, each based on analysis of up to 20.3 fb−1 of proton-proton collision data at the centre-of-mass energy of s√ = 7 and 8 TeV at the Large Hadron Collider. The results are interpreted in the context of the 19-parameter phenomenological minimal supersymmetric standard model, in which the lightest supersymmetric particle is a neutralino, taking into account constraints from previous precision electroweak and flavour measurements as well as from dark matter related measurements. The results are presented in terms of constraints on supersymmetric particle masses and are compared to limits from simplified models. The impact of ATLAS searches on parameters such as the dark matter relic density, the couplings of the observed Higgs boson, and the degree of electroweak fine-tuning is also shown. Spectra for surviving supersymmetry model points with low fine-tunings are presented.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: Since the top quark FCNC processes are extremely supressed in the Standard Model (SM) but could be greatly enhanced in some new physics models, they could serve as a smoking gun for new physics hunting at the LHC. In this brief review we summarize the new physics predictions for various top quark FCNC processes at the LHC by focusing on two typical models: the minimal supersymmetric model (MSSM) and the topcolor-assisted technicol or (TC2) model. The conclusion is: (1) Both new physics models can greatly enhance the SM predictions by several orders; (2) The TC2 model allows for largest enhancement, and for each channel the maximal prediction is much larger than in the MSSM; (3) Compared with the 3 sigma sensitivity at the LHC, only a couple of channels are accessible for the MSSM while most channles are accesible for the TC2 model.
分类: 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We briefly review the lepton flavor violating Z-decays at GigaZ as a probe of supersymmetry by focusing on Z → lilj in two representative supersymmetric models: the minimal supersymmetric model without R-parity and the supersymmetric seesaw model. We conclude that under the current experimental constraints from LEP and li → ljγ, these rare decays can still be enhanced to reach the sensitivity of the GigaZ. Therefore, supersymmetry can be probed via these decays at GigaZ.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: This paper briefly reviews the lepton flavor violating Z-decays at GigaZ as a probe of supersymmetry by focusing on Z -> l(i)(l) over bar (j) in two representative supersymmetric models: the minimal supersymmetric model without R-parity and the supersymmetric seesaw model. The work concludes that under the current experimental constraints from LEP and l(i) -> l(j)gamma, these rare decays can still be enhanced to reach the sensitivity of the GigaZ. Therefore, supersymmetry can be probed via these decays at GigaZ.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We briefly review the supersymmetric explanation for the cosmic dark matter. Although the neutralino in the minimal supersymmetric model (MSSM), the next-to-minimal supersymmetric model (NMSSM) and the nearly minimal supersymmetric model (nMSSM) can naturally explain the dark matter relic density, the PAMELA result can hardly be explained in these popular models. In the general singlet extension of the MSSM,both the PAMELA result and the relic density can be explained by the singlino-like neutralino. Such singlino-like neutralinos annihilate into the singlet-like Higgs bosons, which are light enough to decay dominantly to muons or electrons, and the annihilation cross section can be greatly enhanced by the Sommerfeld effect via exchanging alight CP-even singlet-like Higgs boson. In this scenario, in order to meet the stringent LEP constraints, the SM-like Higgs boson tends to decay into the singlet Higgs pairs instead of b (b) over bar and consequently it will give a multi-muon signal h(SM) -> aa -> 4 mu or h(SM) -> hh -> 4a -> 8 mu at the LHC.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-14
摘要: To obtain a standard model-like Higgs boson around 125 GeV in the minimal supersymmetric standard model with minimal gauge mediation of supersymmetry breaking (GMSB), a heavy stop at multi-TeV level is needed and incurs severe fine-tuning, which can be ameliorated in the framework of the deformed GMSB with visible-hidden direct Yukawa interactions (YGMSB). We examine some general features of the YGMSB and focus on the scenario with Higgs-messenger couplings (HYGMSB) which can automatically maintain the minimal flavor violation. It turns out that such a Yukawa mediation scenario can give a large -Lambda(t) and -m((t) over tildeL,R)(2), leading to a maximal stop mixing, and thus can readily give a light stop ((t) over tilde (1)) below the TeV scale. However, we find that in the minimal HYGMSB scenario, m(Hu)(2) is too large and then the electroweak symmetry breaking is inconsistent with the large stop mixing. To solve this problem, we modify the hidden sectors in two ways, adding a new strong gauge dynamics or introducing the (10, (10) over bar) messengers. For each case we present some numerical studies.
分类: 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-27
摘要: In this note we revisit the SUSY effects in Rb under current experimental constraints including the LHC Higgs data, the B -physics measurements, the dark matter relic density and direct detection limits, as well as the precision electroweak data. We first
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-17
摘要: We calculate the dependence on intermediate scale of the gaugino mass ratios upon breaking of SO(10) into the SM via an intermediate group H. We see that the ratios change significantly when the intermediatescale is low (say, 108 GeV or 1 Tev) compared to the case when the two breakings occur at thesame scale.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: The heavy gravitino in the minimal supergravity (mSUGRA) models is likely to be the lightest supersymmetric particle (LSP). Produced from the late decays of the metastable weakly interacting massive particles (WIMPS) such as the lightest neutralinos, the stable gravitinos can be plausible candidates for the cold dark matter in the universe. Such gravitino dark matter can naturally evade the current detection experiments due to its superweak couplings. However, this scenario must be subjected to the constraints from the big bang nucleosynthesis (BBN) predictions for light element abundances as well as the Wilkinson microwave anisotropy probe (WMAP) data for the relic density. Assuming the popular case in which the lightest neutralino is the next-to-lightest supersymmetric particle (NLSP), we find that requiring BBN predictions for light element abundances to agree with the WMAP data can impose upper and lower mass bounds on both the gravitino LSP and the neutralino NLSP. A scan over the mSUGRA parameter space, subjected to the BBN constraints, the WMAP data and the b --> sgamma bounds, shows that the low tan beta (less than or similar to 40) region as well as the region accessible at the CERN Large Hadron Collider (LHC) will be severely constrained. Such stringent constraints on the parameter space might be instructive for testing this scenario in future collider experiments.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-14
摘要: 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.
分类: 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We investigate a strategy to search for light, nearly degenerate higgsinos within the natural MSSM at the LHC. We demonstrate that the higgsino mass range μμ\mu in 100?150100?150100-150 GeV, which is preferred by the naturalness, can be probed at 2σ2σ2\si
分类: 物理学 >> 核物理学 提交时间: 2017-07-30
摘要: Symmetry plays a fundamental role in physics. The quasi-degeneracy between single-particle orbitals (n, l, j = l + 1/2) and (n − 1, l + 2, j = l + 3/2) indicates a hidden symmetry in atomic nuclei, the so-called pseudospin symmetry (PSS). Since the introduction of the concept of PSS in atomic nuclei, there have been comprehensive efforts to understand its origin. Both splittings of spin doublets and pseudospin doublets play critical roles in the evolution of magic numbers in exotic nuclei discovered by modern spectroscopic studies with radioactive ion beam facilities. Since the PSS was recognized as a relativistic symmetry in 1990s, many special features, including the spin symmetry (SS) for anti-nucleon, and many new concepts have been introduced. In the present Review, we focus on the recent progress on the PSS and SS in various systems and potentials, including extensions of the PSS study from stable to exotic nuclei, from non-confining to confining potentials, from local to non-local potentials, from central to tensor potentials, from bound to resonant states, from nucleon to anti-nucleon spectra, from nucleon to hyperon spectra, and from spherical to deformed nuclei. Open issues in this field are also discussed in detail, including the perturbative nature, the supersymmetric representation with similarity renormalization group, and the puzzle of intruder states.
分类: 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: In this talk we briefly review the current CDMS/XENON constraints on the neutralino dark matter in three popular supersymmetric models: the minimal (MSSM), the next-to-minimal (NMSSM) and the nearly minimal (nMSSM). The constraints from the dark matter re
分类: 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We propose a deflected anomaly mediation scenario from SUSY QCD which can lead to both positive and negative deflection parameters (there is a smooth transition between these two deflection parameter regions by adjusting certain couplings). Such a scenario can naturally give a SUSY spectrum in which all the colored sparticles are heavy while the sleptons are light. As a result, the discrepancy between the Brookheaven gμ − 2 experiment and LHC data can be reconciled in this scenario. We also find that the parameter space for explaining the gμ − 2 anomaly at 1σ level can be fully covered by the future LUX-ZEPLIN 7.2 Ton experiment.