所有结果

分类： 物理学 >> 基本粒子与场物理学

Kibble mechanism drastically underestimates the production of point-like topological defects, as confirmed recently in atomic and condensed matter systems If non-thermally produced, they can be cosmological dark matter of mass 1-10 PeV or heavier If thermalized, skyrimon of mass 1-10 TeV is also a viable dark matter candidate, whose decay may explain e(+/-) spectra in cosmic rays recently measured by PAMELA, FERMI, and HESS Collaborations Models that produce magnetic monopoles below the inflation scale, such as Pati-Salam unification, are ruled out unless new annihilation mechanism for monopoles is introduced (C) 2010 Elsevier B V All rights reserved |

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. |

Computations of superstring amplitudes in pure spinor formalism via Cadabra

Sun, Kesheng; Ding, Xiangmao; Sun, Fei; Zhang, Haibin分类： 物理学 >> 基本粒子与场物理学

In this paper, we will illustrate how computer algebra system Cadabra is used in computing the supersymmetric amplitude in pure spinor formalism and provide the source code that computes the tree-level massless 5-gluon amplitude. |

分类： 物理学 >> 凝聚态:结构、力学和热性能

A robust solid state diffusion joining technique for SiC ceramics was designed with thickness-controlled Ti interlayer formed by Physical Vapor Deposition method and joined by Electric Field-Assisted Sintering Technology. The interface reaction and phase revolution process were investigated in details, and was analyzed in term of equilibrium phase diagram and also concentration-dependent potential diagram of Ti-Si-C ternary system. Interestingly, on the same joining conditions (fixed temperature and annealing duration), the thickness of Ti interlayer determined the concentration and distribution of reactants of Si and C elements in the resultant joint layer, and the respective diffusion distance of Si and C into Ti interlayer dramatically differentiated during the short joining process (only 5 min). In the case of 100nm thickness Ti interlayer, the C concentration saturated quickly in the joint layer and benefited the formation of TiC phase and following Ti3SiC2 phase. When the Ti thickness increase to 1μm, Si atoms easily diffuse through the diluted Ti-C alloy (dense TiC phase not formed), and amount of Ti5Si3 brittle phase was preferential formed. When the thickness of Ti interlayer is 100nm, SiC ceramics were successfully joined at low temperature of 1000°C for 20min with a flexural strength of 168.2MPa which satisfies the application in corrosion environment. All above findings revealed the importance of diffusion kinetics of reactants on the final composition in the solid state reaction, especially in the joining technique for the covalent SiC ceramics. The well-controlled composition in the joint layer of SiC couples will find its application merits in the harsh service environments, such as nuclear cladding for accident-tolerant fuel (ATF) in the environment of steam corrosion, high neutron irradiation, high temperature, etc.). |

An efficient m-step Levenberg-Marquardt method for nonlinear equations

Chen, Liang; Ma, Yanfang; Su, Chencheng分类： 数学 >> 控制和优化

In this paper, we construct and analyze an efficient m-step Levenberg-Marquardt method for nonlinear equations. The main advantage of this method is that the m-step LM method could save more Jacobian calculations with frozen $(J_k^TJ_k+\lambda_kI)^{-1}J_k^T$ at every iteration. Under the local error bound condition which is weaker than nonsingularity, the m-step LM method has been proved to have $(m+1)$th convergence order. The global convergence has also been given by trust region technique. Numerical results show that the m-step LM method is efficient and could save many calculations of the Jacobian especially for large scale problems. |

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. |