All Results

Status of Natural Supersymmetry from the GmSUGRA in Light of the current LHC Run-2 and LUX data

Waqas Ahmed; Xiao-Jun Bi; Tianjun Li; Jia Shu Niu; Shabbar Raza; Qian-Fei Xiang; Peng-Fei YinSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We study natural supersymmetry in the Generalized Minimal Supergravity (GmSUGRA).For the parameter space with low energy electroweak fine-tuning measures less than 50, we are left with only the Z-pole, Higgs-pole and Higgsino LSP scenarios for dark matter (DM). We perform the focused scans for such parameter space and find that it satisfies various phenomenological constraints and is compatible with the current direct detection bound on neutralino DM reported by the LUX experiment. Such parameter space also has solutions with correct DM relic density besides the solutions with DM relic density smaller or larger than 5 WMAP9 bounds. We present five benchmark points as examples. In these benchmark points, gluino and the first two generations of squarks are heavier than 2 TeV, stop ?t1,2 are in the mass range [1, 2] TeV, while sleptons are lighter than 1 TeV. Some part of the parameter space can explain the muon anomalous magnetic moment within 3 as well. We also perform the collider study of such solutions by implementing and comparing with relevant studies done by the ATLAS and CMS Collaborations. We find that the points with Higgsino dominant ? 02/ ? ±1 mass upto 300 GeV are excluded in Z-pole scenario while for Higgs-pole scenario, the points with ? 02 mass up to 460 GeV are excluded. We also notice that the Higgsino LSP points in our present scans are beyond the reach of present LHC searches. Next, we show that for both the Z-pole and Higgs-pole scenarios, the points with electroweak fine-tuning measure around 20 do still survive. |

submitted time
2017-11-10
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A systematic study on the cosmic ray antiproton ?ux

Su-Jie Lin; Xiao-Jun Bi; Jie Feng; Peng-Fei Yin; Zhao-Huan YuSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Recently the AMS-02 collaboration has published the measurement of the cosmic antiproton to proton ratio p?/p and the p? ?ux with a high precision up to ? 450 GeV. In this work, we perform a systematic analysis of the secondary antiproton ?ux generated by the cosmic ray interaction with the interstellar gas. The uncertainty of the prediction originates from the cosmic ray propagation process and the hadronic interaction models. Although the cosmic ray propagation parameters have been well controlled by the AMS-02 B/C ratio data for a speci?ed model, di?erent propagation models can not be discriminated by the B/C data. The p? ?ux is also calculated for several hadronic interaction models, which are generally adopted by the cosmic ray community. However, the results for di?erent hadronic models do not converge. We ?nd the EPOS LHC model, which seems to ?t the collider data very well, predicts a slightly lower p?/p ratio than the AMS-02 data at the high energy end. Finally we derive the constraints on the dark matter annihilation cross section from the AMS-02 p?/p ratio for di?erent propagation and hadronic interaction models. |

Perspective on the cosmic-ray electron spectrum above TeV

Kun Fang; Bing-Bing Wang; Xiao-Jun Bi; Su-Jie Lin; Peng-Fei YinSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The AMS-02 has measured the cosmic ray electron (plus positron) spectrum up to ?TeV with an unprecedent precision. The spectrum can be well described by a power law without any obvious features above 10 GeV. The satellite instrument Dark Matter Particle Explorer (DAMPE), which was launched a year ago, will measure the electron spectrum up to 10 TeV with a high energy resolution. The cosmic electrons beyond TeV may be attributed to few local cosmic ray sources, such as supernova remnants. Therefore, spectral features, such as cuto? and bumps, can be expected at high energies. In this work we give a careful study on the perspective of the electron spectrum beyond TeV. We ?rst examine our astrophysical source models on the latest leptonic data of AMS-02 to give a self-consistent picture. Then we focus on the discussion about the candidate sources which could be electron contributors above TeV. Depending on the properties of the local sources (especially on the nature of Vela), DAMPE may detect interesting features in the electron spectrum above TeV in the future. |

Excesses of Cosmic Ray Spectra from A Single Nearby Source

Wei Liu; Xiao-Jun Bi; Su-Jie Lin; Bing-Bing Wang; Peng-Fei YinSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Growing evidence reveals universal hardening on various cosmic ray spectra, e.g. proton, positron, as well as antiproton fraction. Such universality may indicate they have a common origin. In this paper, we argue that these widespread excesses can be accounted for by a nearby supernova remnant surrounded by a giant molecular cloud. Secondary cosmic rays (p, e+) are produced through the collisions between the primary cosmic ray nuclei from this supernova remnant and the molecular gas. Different from the background, which is produced by the ensemble of large amount of sources in the Milky Way, the local injected spectrum can be harder. The time-dependent transport of particles would make the propagated spectrum even harder. Under this scenario, the anomalies of both primary (p, e?) and secondary (e+, ?p/p) cosmic rays can be properly interpreted. We further show that the TeV to sub-PeV anisotropy of proton is consistent with the observations if the local source is relatively young and lying at the anti-Galactic center direction. |

The interpretation for Galactic Center Excess and Electroweak Phase Transition in the NMSSM

Xiao-Jun Bi; Ligong Bian; Weicong Huang; Jing Shu; Peng-Fei YinSubjects: Physics >> The Physics of Elementary Particles and Fields

The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to b ?b via a light pseudoscalar in the NMSSM. It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly first order phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the tree-level effect in the NMSSM. We find that the annihilation of Singlino/Higgsino DM particles occurring close to the light pseudoscalar resonance is favored by the galactic center excess and the observed DM relic density, and a resulting small κ/λ and a negative Aκ can also lead to a successful strongly first order electroweak phase transition |

The 750 GeV diphoton excess at the LHC and dark matter constraints

Xiao-Jun Bi; Qian-Fei Xiang; Peng-Fei Yin; Zhao-Huan YuSubjects: Physics >> Nuclear Physics

The recent reported 750 GeV diphoton excess at the 13 TeV LHC is explained in the framework of effective field theory assuming the diphoton resonance is a scalar (pseudoscalar) particle. It is found that the large production rate and the broad width of this resonance are hard to simultaneously explain if only visible final states are considered. Therefore an invisible decay channel to dark matter (DM) is strongly favored by the diphoton excess with a broad width, given a large coupling of the new scalar to DM. We set constraints on the parameter space in this scenario using the results from LHC Run 1, DM relic density, and DM direct and indirect detection experiments. We find that the DM searches can exclude a large portion of the parameter regions accounting for the diphoton excess with a broad width. |

submitted time
2016-09-19
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Subjects: Physics >> Nuclear Physics

We study the collider phenomenology of the electroweak phase transition and electroweak baryogenesis in the framework of the effective field theory. Our study shows that the effective theory using the dimension-6 operators can enforce strong first order phase transition and provide sizable CP violation to realize a successful electroweak baryogenesis. Such dimension-6 operators can induce interesting Higgs phenomenology that can be verified at colliders such as the LHC and the planning CEPC. We then demonstrate that this effective theory can originate from vector-like quarks and the triplet Higgs. |

Implications for dark matter annihilation from the AMS-02 $\barp/p$ ratio

Su-Jie Lin; Xiao-Jun Bi; Peng-Fei Yin; Zhao-Huan YuSubjects: Physics >> Nuclear Physics

The AMS-02 collaboration has just released the cosmic antiproton to proton ratio?p?/p?with a high precision up to??450?GeV. In this work, we calculate the secondary antiprotons generated by cosmic ray interactions with the interstellar medium taking into account the uncertainties from the cosmic ray propagation. The?p?/p?ratio predicted by these processes shows some tension with the AMS-02 data in some regions of propagation parameters, but the excess is not significant. We then try to derive upper bounds on the dark matter annihilation cross section from the?p?/p?data or signal regions favored by the data. It is shown that the constraint derived by the AMS-02 data is similar to that from Fermi-LAT observations of dwarf galaxies. The signal region for dark matter is usually required?mχ?O(10)?TeV and?$\left<\sigma v\right>\sim\mathcal{O}(10^{-23})~\cm^3~\sec^{-1}$. |

Interpretation of the Galactic Center excess and electroweak phase transition in the NMSSM

Xiao-Jun Bi; Ligong Bian; Weicong Huang; Jing Shu; Peng-Fei YinSubjects: Physics >> Nuclear Physics

The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to?bb??via a light pseudoscalar in the NMSSM. It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly first order phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the tree-level effect in the NMSSM. We find that the annihilation of Singlino/Higgsino DM particles occurring close to the light pseudoscalar resonance is favored by the galactic center excess and the observed DM relic density, and a resulting small?κ/λ?and a negative?Aκ?can also lead to a successful strongly first order electroweak phase transition. |

Searches for dark matter signals in simplified models at future hadron colliders

Qian-Fei Xiang; Xiao-Jun Bi; Peng-Fei Yin; Zhao-Huan YuSubjects: Physics >> Nuclear Physics

We study the prospect of dark matter (DM) searches in the monojet channel at future?pp?colliders with center-of-mass energies of 33, 50, and 100~TeV. We consider a class of simplified models in which a vector boson connecting DM particles to quarks is introduced. Comparing with studies in the effective field theory, the present framework gives more reasonable production rates and kinematics of the DM signatures. We estimate the sensitivities of future colliders with an integrated luminosity of 3?ab?1?to the DM-induced monojet signature and show the parameter space that can be explored. The constraints from direct and indirect DM detection experiments are compared with the future collider sensitivities. We find that the future collider detection will be much more sensitive than the indirect detection for the vector interaction, and have better sensitivities than those of the direct detection by several orders of magnitude for the axial vector interaction. |