所有结果

TeV scale horizontal gauge symmetry and its implications in B-physics

Seong Chan Park; Jing Shu; Kai Wang; Tsutomu T. Yanagida分类： 物理学 >> 基本粒子与场物理学

We propose a gauged U(1)H horizontal symmetry around TeV scale that is a subgroup of a SU(3)H horizontal gauge symmetry broken at O(1014) GeV. The breaking generates right-handed Majorana neutrino masses through a SU(3)H sextet scalar. A particular Majorana right-handed neutrino mass matrix explicitly determines the remnant U(1)H at low energy which only couples to b−s and µ−τ in the gauge eigenstate. The dangerous K − K¯ , D − D¯ mixing and Bs → µ +µ − are kept to be safe because the relevant couplings are suppressed through high powers of small mixing angles in the fermion rotation matrix. Our analysis which applies to the general case shows that the Tevatron di-muon anomaly can be explained through the Bs and Bd mixing while keeping all the other experimental constraints within 90 % C. L. For the B meson decay, the Bs → µ ±τ ∓ is the leading leptonic decay channel which is several orders of magnitude below current experimental bound |

A Revisit to Top Quark Forward-Backward Asymmetry

Jing Shu; Kai Wang; Guohuai Zhu分类： 物理学 >> 基本粒子与场物理学

We analyze various models for the top quark forward-backward asymmetry ( A t F B) at the Tevatron, using the latest CDF measurements on different At F Bs and the total cross section. The axigluon model in Ref. [5] has difficulties in explaining the large rapidity dependent asymmetry and mass dependent asymmetry simultaneously and the parameter space relevant to A t F B is ruled out by the latest dijet search at ATLAS. In contrast to Ref. [8], we demonstrate that the large parameter space in this model with a U(1) d flavor symemtry is not ruled out by flavor physics. The t-channel flavor-violating Z ′ , W ′ and diquark models all have parameter regions that satisfy different AF B measurements within 1 σ. However, the heavy Z ′ model which can be marginally consistent with the total cross section is severely constrained by the Tevatron direct search of samesign top quark pair. The diquark model suffers from too large total cross section and is difficult to fit the t t¯ invariant mass distribution. The electroweak precision constraints on the W ′ model based on Z ′ - Z mixings is estimated and the result is rather weak ( m Z ′ > 450 GeV). Therefore, the heavy W ′ model seems to give the best fit for all the measurements. The W ′ model predicts the t t¯ + j signal from tW ′ production and is 10%-50% of SM t t¯ at the 7 TeV LHC. Such t + j resonance can serve as the direct test of the W ′ model. |

Disentangling Strong Dynamics through Quantum Interferometry

Hitoshi Murayama; Vikram Rentala; Jing Shu分类： 物理学 >> 基本粒子与场物理学

We present a new probe of strongly coupled electroweak symmetry breaking at the 14 TeV LHC by measuring a phase shift in the event distribution of the decay azimuthal angles in massive gauge boson scattering. One generically expects a large phase shift in the longitudinal gauge boson scattering amplitude due to the presence of broad resonances. This phase shift is observable as an interference effect between the strongly interacting longitudinal modes and the transverse modes of the gauge bosons. We find that even very broad resonances of masses up to 900 GeV can be probed at 3σ significance with a 3000 fb−1 run of the LHC by using this technique. We also present the estimated reach for a future 50 TeV proton-proton collider. |

New Insights of Electroweak Phase Transition in NMSSM

Weicong Huang; Zhaofeng Kang; Jing Shu; Peiwen Wu; Jin Min Yang分类： 物理学 >> 基本粒子与场物理学

: We perform a detailed semi-analytical analysis of the electroweak phase transition (EWPT) property in NMSSM, which serves as a good benchmark model in which the 126 GeV Higgs mixes with a singlet. In this case, a strongly first order electroweak phase transition (SFOEWPT) is achieved by the tree-level effects and the phase transition strength γc is determined by the vacua energy gap at T = 0. We make an anatomy of the energy gap at both tree-level and loop-level and extract out a dimensionless phase transition parameter Rκ ≡ 4κvs/Aκ, which can replace Aκ in the parameterization and affect the light CP odd and even Higgs spectra. We find that SFOEWPT only occurs in Rκ ∼ −1 and positive Rκ . O(10), which in the non-PQ limit case would prefer either a relatively light CP odd or CP even Higgs boson ∼ (60, 100) GeV, therefore serves as a smoking gun signal and requires new search strategies at the LHC. |

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

Ligong Bian; Tao Liu; Jing Shu分类： 物理学 >> 基本粒子与场物理学

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 Wang分类： 物理学 >> 基本粒子与场物理学

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 Yin分类： 物理学 >> 基本粒子与场物理学

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 Zhang分类： 物理学 >> 基本粒子与场物理学

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. |

CP violation from spin–1 resonances in a left–right dynamical Higgs context

Kunming Ruan; Jing Shu; Juan Yepes分类： 物理学 >> 基本粒子与场物理学

New physics field content in the nature, more specifically, from spin–1 resonances sourced by the extension of the SM local gauge symmetry to the larger local group SU(2)L⊗SU(2)R⊗U(1)B−L, may induce CP–violation signalling NP effects from higher energy regimes. In this work we completely list and study all the CP–violating operators up to the p4–order in the Lagrangian expansion, for a non–linear left–right electroweak chiral context and coupled to a light dynamical Higgs. Heavy right handed fields can be integrated out from the physical spectrum, inducing thus a physical impact in the effective gauge couplings, fermionic electric dipole moment, and CP-violation in the decay h → ZZ∗ → 4 l that are briefly analysed. The final relevant set of effective operators have also been identified at low energies. |

Low Scale Composite Higgs Model and 1.8 ∼ 2 TeV Diboson Excess

Ligong Bian Da Liu; Jing Shu1分类： 物理学 >> 基本粒子与场物理学

We consider a simple solution to explain the recent diboson excess observed by ATALS and CMS Collaborations in models with custodial symmetry SU(2)L ×SU(2)R → SU(2)c. The SU(2)L triplet vector boson ρ with mass range of 1.8 ∼ 2 TeV would be produced through the Drell-Yan process with sizable diboson decay branching to account for the excess. The other SU(2)L × SU(2)R bidoublet axial vector boson a would cancel all deviations of electroweak obervables induced by ρ even if the SM fermions mix with some heavy vector like (composite) fermions which couple to ρ (“non-universally partially composite”), therefore allows arbitrary couplings between each SM fermion and ρ. We present our model in the “General Composite Higgs” framework with SO(5) × U(1)X → SO(4) × U(1)X breaking at scale f and demand the first Weinberg sum rule and positive gauge boson form factors as the theoretical constraints. We find that our model can fit the diboson excess very well if the left-handed SM light quarks, charged leptons and tops have zero, zero/moderately small and moderate/large composite components for reasonable values of gρ and f. The correlation between tree level S parameter and the h → Zγ suggest a large a contribution to h → Zγ and it is indeed a O(1) effect in our parameter space which provides a strong hint for our scenario if this diboson excess is confirmed by the 13 ∼ 14 TeV LHC Run II. |