We examine the parameter space of the constrained MSSM by considering various experimental constraints. For the dark matter sector, we require the neutralino dark matter to account for the relic density measured by the WMAP and satisfy the XENON limits on its scattering rate with the nucleon. For the collider constraints, we consider all relevant direct and indirect limits from LEP, Tevatron and LHC as well as the muon anomalous magnetic moment. Especially, for the limits from Bs→μ+μ−, we either directly consider its branching ratio with the latest LHC data or alternatively consider the double ratio of the purely leptonic decays defined by Br(Bs→μ+μ−)/Br(Bμ→τντ)Br(Ds→τντ)/Br(D→τμτ). We find that under these constraints, the mass of the lightest Higgs boson (h) in both the CMSSM and the NUHM2 is upper bounded by about 124 GeV (126 GeV) before (after) considering its theoretical uncertainty. We also find that for these models the di-photon Higgs signal at the LHC is suppressed relative to the SM prediction, and that the lower bound of the top-squark mass goes up with mh, reaching 600 GeV for mh=124 GeV.

Confronted with the LHC data of a Higgs boson around 125 GeV, different models of low energy SUSY show different behaviors: some are favored, some are marginally survived and some are strongly disfavored or excluded. In this note we update our previous scan over the parameter space of various low energy SUSY models by considering the latest experimental limits like the LHCb data for B s → μ + μ − and the XENON 100 (2012) data for dark matter-nucleon scattering. Then we confront the predicted properties of the SM-like Higgs boson in each model with the combined 7TeV and 8TeV Higgs search data ofthe LHC. For a SM-like Higgs boson around 125 GeV, we have the following observations: (i) The most favored model is the NMSSM, whose predictions about the Higgs boson can naturally (without any fine tuning) agree with the experimental data at 1σ level, better than the SM; (ii) The MSSM can fit the LHC data quite well but suffer from some extent of fine tuning; (iii) The nMSSM is excluded at 3σ level after considering all the available Higgs data; (iv) The CMSSM is quite disfavored since it is hard to give a 125 GeV Higgs boson mass and at the same time cannot enhance the di-photon signal rate.

The top quark forward-backward asymmetry AtFB measured at the Tevatron is above the standard model prediction by more than 2σ deviation, which might be a harbinger for new physics. In this work we examine the contribution to AtFB in two different new physics models: one is the minimal supersymmetric model without R parity which contributes to AtFB via sparticle-mediated t channel process d¯d→t¯t; the other is the third-generation enhanced left-right model which contributes to AtFB via Z′-mediated t channel or s channel processes. We find that in the parameter space allowed by the t¯t production rate and the t¯t invariant mass distribution at the Tevatron, the left-right model can enhance AtFB to within the 2σ region of the Tevatron data for the major part of the parameter space, and in optimal case AtFB can reach 12% which is slightly below the 1σ lower bound. For the minimal supersymmetric model without R parity, only in a narrow part of the parameter space can the λ'' couplings enhance AtFB to within the 2σ region while the λ′ couplings just produce negative contributions to worsen the fit.

The anomaly of the top quark forward-backward asymmetry AtFB observed at the Tevatron can be explained by the t-channel exchange of a neutral gauge boson (Z′) which has sizable flavor-changing coupling for top and up quarks. This gauge boson can also induce the top quark flavor-changing neutral-current (FCNC) decays and the like-sign top pair production at the LHC. In this work, we focus on two models which predict such a Z′, namely, the left-right model and the U(1)X model, to investigate the correlated effects on AtFB, the FCNC decays t→uV (V=g, Z, γ) and the like-sign top pair production at the LHC. We also pay special attention to the most recently measured AtFB in the large top pair invariant mass region. We find that under the current experimental constraints both models can alleviate the deviation of AtFB and, meanwhile, enhance the like-sign top pair production to the detectable level of the LHC. We also find that the two models give different predictions for the observables and their correlations, and thus they may even be distinguished by jointly studying these top quark observables.

As the most important discovery channel for a light Higgs boson at the LHC, the di-photon signal gg→h→γγ is sensitive to underlying physics. In this work we investigate such a signal in a comparative way by considering three different supersymmetric models, namely the minimal supersymmetric standard model (MSSM), the next-to-minimal supersymmetric standard model (NMSSM) and the nearly minimal supersymmetric standard model (nMSSM). Under the current collider and cosmological constraints we scan over the parameter space and obtain the following observation in the allowed parameter space: (i) In the nMSSM the signal rate is always suppressed; (ii) In the MSSM the signal rate is suppressed in most cases, but in a tiny corner of the parameter space it can be enhanced (maximally by a factor of 2); (iii) In the NMSSM the signal rate can be enhanced or suppressed depending on the parameter space, and the enhancement factor can be as large as 7.