All Results

Energy Level Statistics of the U(5) and O(6) Symmetries in the Interacting Boson Model

Jing Shu; Ying Ran; Tao Ji; Yu-xin LiuSubjects: Physics >> The Physics of Elementary Particles and Fields

We study the energy level statistics of the states in U(5) and O(6) dynamical symmetries of the interacting boson model and the high spin states with backbending in U(5) symmetry. In the calculations, the degeneracy resulting from the additional quantum number is eliminated manually. The calculated results indicate that the finite boson number N effect is prominent. When N has a value close to a realistic one, increasing the interaction strength of subgroup O(5) makes the statistics vary from Poisson-type to GOE-type and further recover to Poisson-type. |

Statistical Properties of E(5) and X(5) Symmetries

Jing Shu; Hong-bo Jia; Yu-xin LiuSubjects: Physics >> The Physics of Elementary Particles and Fields

We study the energy level statistics of the states in E(5) and X(5) dynamical symmetries. The calculated results indicate that the statistics of E(5) symmetry is regular and follows Poisson statistics, while that of X(5) symmetry involves two maxima in the nearest neighbor level spacing distribution P(s) and the ?3 statistics follows the GOE statistics. It provides an evidence that the X(5) symmetry is at the critical point exhibiting competing degrees of freedom |

Models of Baryogenesis via Spontaneous Lorentz Violation

Sean M. Carroll; Jing ShuSubjects: Physics >> The Physics of Elementary Particles and Fields

In the presence of background fields that spontaneously violate Lorentz invariance, a matter-antimatter asymmetry can be generated even in thermal equilibrium. In this paper we systematically investigate models of this type, showing that either high-energy or electroweak versions of baryogenesis are possible, depending on the dynamics of the Lorentz-violating fields. In addition to the previously-studied models of spontaneous baryogenesis and quintessential baryogenesis, we identify two scenarios of interest: baryogenesis from a weak-scale pseudo-Nambu-Goldstone boson with intermediate-scale baryon-number violation, and sphaleron-induced baryogenesis driven by a constant-magnitude vector with a late-time phase transition. |

Baryogenesis from an Earlier Phase Transition

Jing Shu; Tim M.P. Tait; Carlos E.M. WagnerSubjects: Physics >> The Physics of Elementary Particles and Fields

We explore the possibility that the observed baryon asymmetry of the universe is the result of an earlier phase transition in which an extended gauge sector breaks down into the SU(3)C × SU(2)L × U(1)Y of the Standard Model. Our prototypical example is the Topflavor model, in which there is a separate SU(2)1 for the third generation from the SU(2)2 felt by the first two generations. We show that the breakdown of SU(2)1 × SU(2)2 → SU(2)L results in lepton number being asymmetrically distributed through-out the three families, and provided the SM electroweak phase transition is not strongly first order, results in a non-zero baryon number, which for parameter choices that can be explored at the LHC, may explain the observed baryon asymmetry. |

Kaluza-Klein Gluons as a Diagnostic of Warped Models

Ben Lillie; Jing Shu; Tim M.P. TaitSubjects: Physics >> The Physics of Elementary Particles and Fields

We study the properties of g 1 , the first excited state of the gluon in representative variants of the Randall Sundrum model with the Standard Model fields in the bulk. We find that measurements of the coupling to light quarks (from the inclusive cross-section for pp → g 1 → tt), the coupling to bottom quarks (from the rate of pp → g 1 b), as well as the overall width, can provide powerful discriminants between the models. In models with large brane kinetic terms, the g 1 resonance can even potentially be discovered decaying into dijets against the large QCD background. We also derive bounds based on existing Tevatron searches for resonant tt production and find that they require Mg 1 & 950 GeV. In addition we explore the pattern of interference between the g 1 signal and the non-resonant SM background, defining an asymmetry parameter for the invariant mass distribution. The interference probes the relative signs of the couplings of the g 1 to light quark pairs and to tt, and thus provides an indication that the top is localized on the other side of the extra dimension from the light quarks, as is typical in the RS framework. |

Unitarity Bounds for New Physics from Axial Coupling at LHC

Jing ShuSubjects: Physics >> The Physics of Elementary Particles and Fields

If a new massive vector boson with nonzero axial couplings to fermions will be observed at LHC, then an upper limit on the scale of new physics could be derived from unitarity of S-matrix. The new physics will involve either new massive fermions, or scalars, or even a strongly coupled sector. We derive a model independent bound on the scale of new physics. If MG/g A < 3 TeV and the fermion is a top quark, the upper limit is 78 TeV. |

Top Compositeness at the Tevatron and LHC

Ben Lillie; Jing Shu; Tim M.P. TaitSubjects: Physics >> The Physics of Elementary Particles and Fields

We explore the possibility that the right-handed top quark is composite. We examine the consequences that compositeness would have on tt production at the Tevatron, and derive a weak constraint on the scale of compositeness of order a few hundred GeV from the tt inclusive cross section. More detailed studies of differential properties of tt production could potentially improve this limit. We find that a composite top can result in an enhancement of the tttt production rate at the LHC (of as much as 103 compared to the Standatd Model four top rate). We explore observables which allow us to extract the four top rate from the backgrounds, and show that the LHC can either discover or constrain top compositeness for wide ranges of parameter space. |

Landau-Yang Theorem and Decays of a Z ′ Boson into Two Z Bosons

Wai-Yee Keung; Ian Low; Jing ShuSubjects: Physics >> The Physics of Elementary Particles and Fields

We study the decay of a Z ′ boson into two Z bosons by extending the Landau-Yang theorem to a parent particle decaying into two Z bosons. For a spin-1 parent the theorem predicts: 1) there are only two possible couplings and 2) the normalized differential cross-section depends on kinematics only through a phase shift in the azimuthal angle between the two decay planes of the Z boson. When the parent is a Z ′ the two possible couplings are anomaly-induced and CP-violating, respectively. At the CERN Large Hadron Collider their effects could be disentangled when both Z bosons decay leptonically |

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

Motivated by the recent observation of the high energy electron and positron excesses in cosmic ray by PAMELA and ATIC/PPB-BETS, we suggest an anomaly-free scenario for the universal extra dimension that localizes the SM quarks and splits the spectrum of KK quarks from KK leptons. When the SM quarks are “well localized” at the boundaries, the most stringent bound of the model (1/R > 510 GeV) comes from the resonance search for the Tevatron dijet channels. Even at the early stage of LHC, one can discover the second KK gluon for masses up to 4 TeV. |

Dark matter and collider phenomenology of split-UED

Chuan-Ren Chen; Mihoko M. Nojiri; Seong Chan Park; Jing Shu; Michihisa TakeuchiSubjects: Physics >> The Physics of Elementary Particles and Fields

We explicitly show that split-universal extra dimension (split-UED), a recently suggested extension of universal extra dimension (UED) model, can nicely explain recent anomalies in cosmic-ray positrons and electrons observed by PAMELA and ATIC/PPB-BETS. Kaluza-Klein (KK) dark matters mainly annihilate into leptons because the hadronic branching fraction is highly suppressed by large KK quark masses and the antiproton flux agrees very well with the observation where no excess is found . The flux of cosmic gamma-rays from pion decay is also highly suppressed and hardly detected in low energy region (Eγ . 20 GeV). Collider signatures of colored KK particles at the LHC, especially q1q1 production, are studied in detail. Due to the large split in masses of KK quarks and other particles, hard pT jets and missing ET are generated, which make it possible to suppress the standard model background and discover the signals. |