All Results

Post-ACME2013 CP-violation in Higgs Physics and Electroweak Baryogenesis

Ligong Bian; Tao Liu; Jing ShuSubjects: Physics >> The Physics of Elementary Particles and Fields

We present a class of cancellation mechanisms to suppress the total contributions of Barr-Zee diagrams to the electron electric dipole moment (eEDM). This class of mechanisms are of particular significance after the new eEDM upper limit, which strongly constrains the allowed magnitude of CP-violation in Higgs couplings and hence the feasibility of electroweak baryogenesis (EWBG), were released by the ACME collaboration in 2013. We point out: if both the CP-odd Higgs-photonphoton (Z boson) and the CP-odd Higgs-electron-positron couplings are turned on, a cancellation may occur either between the contributions of a CP-mixing Higgs boson, with the other Higgs bosons being decoupled, or between the contributions of a CP-even and a CP-odd Higgs bosons. With the assistance of the cancellation mechanisms, a large CP-phase in Higgs couplings with viable electroweak baryogenesis (EWBG) is still allowed. The reopened parameter regions would be probed by the future neutron, mercury EDM measurements, and direct measurements of Higgs CP-properties at the LHC and future colliders. |

Two component dark matter with multi-Higgs

Ligong Bian; Tianjun Li; Jing ShuXiao-Chuan WangSubjects: Physics >> The Physics of Elementary Particles and Fields

With the assistance of two extra groups, i.e., an extra hidden gauge group SU(2)D and a global U(1) group, we propose a two component dark matter (DM) model. After the symmetry SU(2)D × U(1) being broken, we obtain both the vector and scalar DM candidates. The two DM candidates communicate with the standard model (SM) via three Higgs as multi-Higgs portals. The three Higgs are mixing states of the SM Higgs, the Higgs of the hidden sector and real part of a supplement complex scalar singlet. We study relic density and direct detection of DM in three scenarios. The resonance behaviors and interplay between the two component DM candidates are represented through investigating of the relic density in the parameter spaces of the two DMs masses. The electroweak precision parameters constrains the two Higgs portals couplings (λm and δ2). The relevant vacuum stability and naturalness problem in the parameter space of λm and δ2 are studied as well. The model could alleviate these two problems in some parameter spaces under the constraints of electroweak precision observables and Higgs indirect search. |

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 |

Prospects for Triple Gauge Coupling Measurements at Future Lepton Colliders and the 14 TeV LHC

Ligong Bian; Jing Shu; Yongchao ZhangSubjects: Physics >> The Physics of Elementary Particles and Fields

The WW production is the primary channel to directly probe the triple gauge couplings. We first analyze the e+e?→W+W? process at the future lepton collider, China’s proposed Circular Electron-Positron Collider (CEPC). We use the five kinematical angles in this process to constrain the anomalous triple gauge couplings and relevant dimension six operators at the CEPC up to the order of magnitude of 10-4. The most sensible information is obtained from the distributions of the production scattering angle and the decay azimuthal angles. We also estimate constraints at the 14 TeV LHC, with both 300 fb?1 and 3000 fb?1 integrated luminosity from the leading lepton pT and azimuthal angle difference ? φll distributions in the di-lepton channel. The constrain is somewhat weaker, up to the order of magnitude of 10?3. The limits on the triple gauge couplings are complementary to those on the electroweak precision observables and Higgs couplings. Our results show that the gap between sensitivities of the electroweak and triple gauge boson precision can be significantly decreased to less than one order of magnitude at the 14 TeV LHC, and that both the two sensitivities can be further improved at the CEPC. |

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

In this work, we introduce an extra singlet pseudoscalar into the Type-III two Higgs doublet model (2HDM) which is supposed to solve a series of problems in the modern particle-cosmology. With existence of a light pseudoscalar, the h → ?τ excess measured at CMS and as well as the (g ? 2)? anomaly could be simultaneously explained within certain parameter spaces that can also tolerate the data on the flavor-violating processes τ → ?γ and Higgs decay gained at LHC. Within the same parameter spaces, the DM relic abundance is well accounted. Moreover, the recently observed Galactic Center gamma ray excess(GCE) is proposed to realize through dark matter(DM) pair annihilations, and in this work, the scenario of the annihilation being mediated by the pseudoscalar is also addressed. |

Interference E#11;ect on Resonance Studies in Searches of Heavy Particles

Ligong Bian; Da Liu; Jing Shu; Yongchao ZhangSubjects: Physics >> The Physics of Elementary Particles and Fields

The interference between resonance signal and continuum background can be either constructive or destructive, depending on the relative sign of couplings between the signal and background amplitudes. Different interference schemes lead to asymmetric distortions of the resonance line shape, which could be distinguished in experiments, when the internal resonance width is larger than the detector resolution. Interpreting the ATLAS diboson excesses by means of a toy W' model as an illustrative example (though it is disfavored by the 13 TeV data), we find that the signs of resonance couplings can only be revealed in the line shape measurements up to a high confidence level at a high luminosity, which could bring us further information on the underlying theory beyond resonance searches at future lepton and hadron colliders. |

A hidden confining world on the 750 GeV diphoton excess

Ligong Bian; Ning Chen; Da Liu; Jing ShuSubjects: Physics >> The Physics of Elementary Particles and Fields

We explain the recent diphoton excesses around 750 GeV by both ATLAS and CMS as a singlet scalar Φ which couples to SM gluon and neutral gauge bosons only through higher dimensional operators. A natural explanation is that Φ is a pseudo-Nambu-Goldstone boson (pNGB) which receives parity violation through anomaly if there exists a hidden strong dynamics. The singlet and other light pNGBs will decay into two SM gauge bosons and even serves as the meta-stable coloured states which can be probed in the future. By accurately measuring their relative decay and the total production rate in the future, we will learn the underlying strong dynamics parameter. The lightest baryon in this confining theory could serve as a viable dark matter candidate. |

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. |

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