所有结果

Models of baryogenesis via spontaneous Lorentz violation

Carroll, Sean M.; Shu, Jing分类： 物理学 >> 基本粒子与场物理学

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

Shu, Jing; Tait, Tim M. P.; Wagner, Carlos E. M.分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

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)xSU(2)(L)xU(1)(Y) of the standard model. Our proto-typical 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)xSU(2)(2)-> SU(2)(L) results in lepton number being asymmetrically distributed throughout the three families, and provided the SM electroweak phase transition is not strongly first order, results in a nonzero baryon number, which for parameter choices that can be explored at the LHC may explain the observed baryon asymmetry. |

Kaluza-Kleingluons as a diagnostic of warped models

Lillie, Ben; Shu, Jing; Tait, Tim M. P.分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

We study the properties of g(1), the first excited state of the gluon in representative variants of the Randall-Sundrum (RS) model with the standard model (SM) fields in the bulk. We find that measurements of the coupling to light quarks (from the inclusive cross section for pp -> g(1)-> t (t) over bar), 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 t (t) over bar production and find that they require M(g)(1)greater than or similar to 950 GeV. In addition, we explore the pattern of interference between the g(1) signal and the nonresonant 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 t (t) over bar, 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. |

Top compositeness at the Tevatron and LHC

Lillie, Ben; Shu, Jing; Tait, Tim M. P.分类： 物理学 >> 基本粒子与场物理学

We explore the possibility that the right-handed top quark is composite. We examine the consequences that compositeness would have on t (t) over bar production at the Tevatron, and derive a weak constraint on the scale of compositeness of order a few hundred GeV from the t (t) over bar inclusive cross section. More detailed studies of differential properties of t (t) over bar production could potentially improve this limit. We find that a composite top can result in an enhancement of the t (t) over bart (t) over bar production rate at the LHC (of as much as 10(3) 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

Keung, Wai-Yee; Low, Ian; Shu, Jing分类： 物理学 >> 基本粒子与场物理学

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 that (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. |

Unitarity bounds for new physics from axial coupling at CERN LHC

Shu, Jing分类： 物理学 >> 基本粒子与场物理学

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 M-G/g(A) < 3 TeV and the fermion is a top quark, the upper limit is 78 TeV. |

Split universal extra dimension and dark matter

Park, Seong Chan; Shu, Jing分类： 物理学 >> 基本粒子与场物理学

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 standard model quarks and splits the spectrum of Kaluza-Klein (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

Chen, Chuan-Ren; Nojiri, Mihoko M.; Park, Seong Chan; Shu, Jing; Takeuchi, Michihisa分类： 物理学 >> 基本粒子与场物理学

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 (E-gamma less than or similar to 20GeV). Collider signatures of colored KK particles at the LHC, especially q(1)q(1) production, are studied in detail. Due to the large split in masses of KK quarks and other particles, hard p(T) jets and missing E-T are generated, which make it possible to suppress the standard model background and discover the signals. |

Higgs mechanism and loop-induced decays of a scalar into two Z bosons

Cao, Qing-Hong; Jackson, C. B.; Keung, Wai-Yee; Low, Ian; Shu, Jing分类： 物理学 >> 基本粒子与场物理学

We discuss general on-shell couplings of a scalar with two Z bosons using an operator analysis. In addition to the operator that originated from the Higgs mechanism, two dimension-five operators, one CP even and one CP odd, are generated only at the loop level. Simple formulas are derived for the differential decay distributions when the Z pair subsequently decays into four leptons by computing the helicity amplitudes, from which it is shown the CP-odd operator merely induces a phase shift in the azimuthal angular distribution between the two decay planes of the Z bosons. We also investigate new physics scenarios giving rise to loop-induced decays of a scalar into the ZZ pair, and argue that the total decay width of such a scalar would be an order-of-magnitude smaller than that of a Higgs boson, should such decays be observed in the early running of the LHC. Therefore, the total decay width alone is a strong indicator of the Higgs nature, or the lack thereof, of a scalar resonance in ZZ final states. In addition, we study the possibility of using the azimuthal angular distribution to disentangle effects among all three operators. |

Axigluon as possible explanation for p(p)over-bar -> t(t)over-bar forward-backward asymmetry

Frampton, Paul H.; Shu, Jing; Wang, Kai分类： 物理学 >> 基本粒子与场物理学

A flavor-nonuniversal chiral color model is introduced. It is used for comparison to the recent data on (p) over barp -> (t) over bart. We concluded that the data are consistent with interpretation as an axigluon exchange within 1 sigma and a unique rise and fall behavior is predicated with regard to the asymmetry A(FB)(t) as a function of t (t) over bar invariant mass, which can distinguish our model from others before one discovers the axigluon resonance. Further aspects of the model are discussed. (C) 2009 Elsevier B.V. All rights reserved. |