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SUSY induced top quark FCNC decay t -> ch after Run I of LHC

Cao, Junjie; Han, Chengcheng; Wu, Lei; Yang, Jin Min; Zhang, MengchaoSubjects: Physics >> The Physics of Elementary Particles and Fields

In light of the Higgs discovery and the nonobservation of sparticles at the LHC, we revisit the supersymmetric theory (SUSY) induced top quark flavor-changing decay into the Higgs boson. We perform a scan over the relevant SUSY parameter space by considering the constraints from the Higgs mass measurement, the LHC search for SUSY, the vacuum stability, the precision electroweak observables as well as B -> X-s gamma. We make the following observations: (1) In the Minimal Supersymmetric Standard Model (MSSM), the branching ratio of t -> ch can only reach 3.0 x 10(-6), which is about one order smaller than previous results obtained before the advent of the LHC. Among the considered constraints, the Higgs mass and the LHC search for sparticles are found to play an important role in limiting the prediction. (2) In the singlet extension of the MSSM, since the squark sector is less constrained by the Higgs mass, the branching ratio of t -> ch can reach the order of 10(-5) in the allowed parameter space. (3) The chiral-conserving mixings delta(LL) and delta(RR) may have remanent effects on t -> ch in the heavy SUSY limit. In the MSSM with squarks above 3 TeV and gluino above 4 TeV and meanwhile the CP-odd Higgs boson mass around 1 TeV, the branching ratio of t -> ch can still reach the order of 10(-8) under the constraints. |

New approach for detecting a compressed bino/wino at the LHC

Han, Chengcheng; Wu, Lei; Yang, Jin Min; Zhang, Mengchao; Zhang, YangSubjects: Physics >> The Physics of Elementary Particles and Fields

In some supersymmetric models like split supersymmetry or models with nonuniversal gaugino mass, 'bino [lightest sparticle (LSP)] and wino [next-to-lightest sparticle (NLSP)] may have rather small mass splitting in order to provide the correct dark matter relic density through bino/wino coannihilation. Such a scenario with the compressed bino/wino is difficult to explore at the LHC. In this work we propose to probe this scenario from pp -> j (chi) over tilde (0)(2)(chi) over tilde (+/-)(1) followed by (chi) over tilde (0)(2) -> gamma(chi) over tilde (0)(1) and (chi) over tilde (+/-)(1) -> W*(chi) over tilde (0)(1) -> l(+/-)nu(chi) over tilde (0)(1) (this method is also applicable to the compressed bino/Higgsino scenario). Through a detailed Monte Carlo simulation for both the signal and the backgrounds, we find that for a mass splitting Delta M similar to 10-15 GeV between bino (LSP) and wino (NLSP), the 14 TeV LHC with a luminosity of 1000 fb(-1) can probe the wino up to 150 GeV (the sensitivity can reach 3.4 sigma for Delta M = 10 GeV and 2 sigma for Delta M = 15 GeV). We also investigate the dark matter detection sensitivities for this scenario and find that the planned XENON-1T (2017) cannot fully cover the parameter space with a wino below 150 GeV allowed by relic density and the LUX limits. |

Higgs self-coupling in the MSSM and NMSSM after the LHC Run 1

Wu, Lei; Yang, Jin Min; Yuan, C. -P.; Zhang, MengchaoSubjects: Physics >> The Physics of Elementary Particles and Fields

Measuring the Higgs self-coupling is one of the crucial physics goals at the LHC Run-2 and other future colliders. In this work, we attempt to figure out the size of SUSY effects on the trilinear self-coupling of the 125 GeV Higgs boson in the MSSM and NMSSM after the LHC Run-1. Taking account of current experimental constraints, such as the Higgs data, flavor constraints, electroweak precision observables and dark matter detections, we obtain the observations: (1) In the MSSM, the ratio lambda(MSSM)(3h)/lambda(SM)(3h) has been tightly constrained by the LHC data, which can be only slightly smaller than 1 and minimally reach 97%; (2) In the NMSSM with lambda < 0.7, a sizable reduction of lambda(MSSM)(3h2)/lambda(SM)(3h2) can occur and minimally reach 10% when the lightest CP-even Higgs boson mass m(h1)., is close to the SM-like Higgs boson m(h2), due to the large mixing angle between the singlet and doublet Higgs bosons; (3) In the NMSSM with lambda > 0.7, a large enhancement or reduction -1.1 < lambda(MSSM)(3h1)/lambda(SM)(3h1) < 2 can occur, which is accompanied by a sizable change of h(1)tau(+)tau(-) coupling. The future colliders, such as the HL-LHC and ILC, will have the capacity to test these large deviations in the NMSSM. (C) 2015 The Authors. Published by Elsevier B.V. |

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

In this paper, we interpret the 750 GeV diphoton excess in the Zee-Babu extension of the two-Higgs-doublet model by introducing a top partner (T)/bottom partner (B). In the alignment limit, the 750 GeV resonance is identified as the heavy CP-even Higgs boson (H), which can be sizably produced via the QCD process pp -> T (T) over bar or pp -> B (B) over bar followed by the decay T -> Ht or B -> Hb. The diphoton decay rate of His greatly enhanced by the charged singlet scalars predicted in the Zee-Babu extension and the total width of H can be as large as 7 GeV. Under the current LHC constraints, we scan the parameter space and find that such an extension can account for the observed diphoton excess. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license. |

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