In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), all singlet-dominated particles including one neutralino, one CP-odd Higgs boson and one CP-even Higgs boson can be simultaneously lighter than about 100 GeV. Consequently, dark matter (DM) in the NMSSM can annihilate into multiple final states to explain the galactic center gamma-ray excess (GCE). In this work we take into account the foreground and background uncertainties for the GCE and investigate these explanations. We carry out a sophisticated scan over the NMSSM parameter space by considering various experimental constraints such as the Higgs data, B-physics observables, DM relic density, LUX experiment and the dSphs constraints. Then for each surviving parameter point we perform a fit to the GCE spectrum by using the correlation matrix that incorporates both the statistical and systematic uncertainties of the measured excess. After examining the properties of the obtained GCE solutions, we conclude that the GCE can be well explained by the pure annihilations χ~01χ~01→bb¯¯ and χ~01χ~01→A1Hi with A 1 being the lighter singlet- dominated CP-odd Higgs boson and H i denoting the singlet-dominated CP-even Higgs boson or SM-like Higgs boson, and it can also be explained by the mixed annihilation χ~01χ~01 →W+W− , A 1 H 1. Among these annihilation channels, χ~01χ~01→A1Hi can provide the best interpretation with the corresponding p-value reaching 0.55. We also discuss to what extent the future DM direct detection experiments can explore the GCE solutions and conclude that the XENON-1T experiment is very promising in testing nearly all the solutions.

We explore the explanation of the Fermi Galactic Center excess (GCE) in the next-to-minimal supersymmetric Standard Model. We systematically consider various experimental constraints including the dark matter (DM) relic density, DM direct detection results, and indirect searches from dwarf galaxies. We find that, for DM with mass ranging from 30 to 40 GeV, the GCE can be explained by the annihilation χχ→a∗→b¯b only when the CP-odd scalar satisfies ma≃2mχ, and in order to obtain the measured DM relic density, a sizable Z-mediated contribution to DM annihilation must intervene in the early universe. As a result, the Higgsino mass μ is upper bounded by about 350 GeV. Detailed Monte Carlo simulations on the 3ℓ+EmissT signal from neutralino/chargino associated production at 14-TeV LHC indicate that the explanation can be mostly (completely) excluded at 95% C.L. with an integrated luminosity of 100(200)  fb−1. We also discuss the implication of possible large Z coupling to DM for the DM-nucleon spin dependent (SD) scattering cross section, and find that although the current experimental bounds on σSDp is less stringent than the spin independent results, the future XENON-1T and LZ data may be capable of testing most parts of the GCE-favored parameter region.

In light of the recent LHC Higgs search data, we investigate the pair production of a SM-like Higgs boson around 125GeV in the MSSM and NMSSM. We first scan the parameter space of each model by considering various experimental constraints, and then calculate the Higgs pair production rate in the allowed parameter space. We find that in most cases the dominant contribution to the Higgs pair production comes from the gluon fusion process and the production rate can be greatly enhanced, maximally 10 times larger than the SM prediction (even for a TeV-scale stop the production rate can still be enhanced by a factor of 1.3). We also calculate the χ 2 value with the current Higgs data and find that in the most favored parameter region the production rate is enhanced by a factor of 1.45 in the MSSM, while in the NMSSM the production rate can be enhanced or suppressed (σ SUSY/σ SM varies from 0.7 to 2.4).

We consider the natural supersymmetry scenario in the framework of the R-parity conserving minimal supersymmetric standard model (called natural MSSM) and examine the observability of stop pair production at the LHC. We first scan the parameters of this scenario under various experimental constraints, including the SM-like Higgs boson mass, the indirect limits from precision electroweak data and B-decays. Then in the allowed parameter space we study the stop pair production at the LHC followed by the stop decay into a top quark plus a lightest neutralino or into a bottom quark plus a chargino. From detailed Monte Carlo simulations of the signals and backgrounds, we find the two decay modes are complementary to each other in probing the stop pair production, and the LHC with s√=14 TeV and 100 fb−1 luminosity is capable of discovering the stop predicted in natural MSSM up to 450 GeV. If no excess events were observed at the LHC, the 95% C.L. exclusion limits of the stop masses can reach around 537 GeV.

Extensions of the standard model often predict new chiral interactions for top quarks, which will contribute to top quark spin correlation and polarization in t¯t production at the LHC. In this work, under the constraints from the current Tevatron measurements, a comparative study of the spin correlation and polarization is performed in three new physics models: the minimal supersymmetric model without R-parity, the third-generation enhanced left-right model, and the axigluon model. We find that the polarization asymmetry may be enhanced to the accessible level in all these models, while the correction to the spin correlation may be detectable in the axigluon model and the minimal supersymmetric model without R-parity with λ'' couplings.

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.

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.

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.

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.

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.