Jun 2013, Volume 8 Issue 3

Cover illustration

  • Dark solitons are localized defects in defocusing systems, and manifest themselves in repulsive Bose–Einstein condensate as a notch in the condensate density and a phase jump across the center. Ring dark solitons are candidates for observing long-time behaviors of 2D dark solitons, and their relevant explorations in the Bose–Einstein condensate began in 2003. It was shown that deeper ring dark solitons inclined to suffer snaking instabilities with a lifetime less [Detail] ...

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    Shou-Hua Zhu
    Miao He

    Neutrinos are elementary particles in the Standard Model. Neutrino oscillation is a quantum mechanical phenomenon beyond the Standard Model. Neutrino oscillation can be described by two independent mass-squared di.erences Δm212, Δm312 (or Δm322) and a3×3 unitary matrix, containing three mixing angles θ12, θ23, θ13, and one charge-parity (CP) phase. θ12 is about 34° and determined by solar neutrino experiments and the reactor neutrino experiment KamLAND. θ23 is about 45° and determined by atmospheric neutrino experiments and accelerator neutrino experiments. θ13 can be measured by either accelerator or reactor neutrino experiments. On Mar. 8, 2012, the Daya Bay Reactor Neutrino Experiment reported the .rst observation of non-zero θ13 with 5.2 standard deviations. In June, with 2.5× previous data, Daya Bay improved the measurement of sin2 2 θ13 = 0.089±0.010(stat)±0.005(syst).

    Pascal Pralavorio, on behalf of the ATLAS Collaboration

    Despite the absence of experimental evidence, weak scale supersymmetry remains one of the best motivated and studied Standard Model extensions. The ATLAS experiment at the LHC searches for signs of supersymmetry in a large variety of signatures involving events with abnormal production of missing transverse momentum, jets, leptons, third generation fermions, gauge bosons or massive long-lived particles. A summary of the most recent results obtained in these searches is presented.

    Adrian Perieanu, on behalf of the CMS Collaboration

    In this paper a review of the results on searches for physics beyond the standard model in pp collisions with the CMS experiment at s = 7 and 8 TeV is presented. Aspects of the analyses and their achieved limits on Z'- and W'-bosons, heavy neutrino, 4th generation, leptoquarks as well as extra dimensions will be covered.

    Gavin J. Davies, on behalf of the CDF and D0 Collaborations

    This article reviews the Higgs searches at the Tevatron, as presented over the summer of 2012; both standard model (SM) and beyond the standard model (BSM) results are discussed as detailed (arXiv: 1207.0449; Phys. Rev. Lett., 2012, 109: 071804; Phys. Rev. D, 2012, 85: 032005).We discuss the combination of searches by the CDF and D0 Collaborations for the standard model Higgs boson in the mass range 100-200 GeV/c2 produced in the the ggH, WH, ZH, tt ˉH, and vector boson fusion production modes, and decaying in the Hbb ˉ, HW + W-, HZZ, Hτ+τ-, and H→γγ modes. The data, collected at the Fermilab Tevatron collider inpp ˉ collisions at s = 1.96 TeV, correspond to integrated luminosities of up to 10 fb-1. In the absence of signal, we expect to exclude the regions 100<mH<120 GeV/c2 and 139<mH<184 GeV/c2. We exclude, at the 95% C.L., two regions: 100<mH<103 GeV/c2, and 147<mH<180 GeV/c2. We observe a signi.cant excess of events in the mass range between 115 and 140 GeV/c2. The local signi.cance corresponds to 3.0 standard deviations at mH =120 GeV/c2; the global signi.cance (incorporating the lookelsewhere e.ect) for such an excess anywhere in the full mass range investigated is approximately 2.5 standard deviations. Furthermore, we separately combine searches for Hbb ˉ, HW + W-and H→γγ. We find that the excess is concentrated in the Hbbˉ channel, appearing in the searches over a broad range of mH; the maximum local significance of 3.3 standard deviations corresponds to a global significance of approximately 3.1 standard deviations. The observed signal strengths in all channels are consistent with the expectation for a standard model Higgs boson at mH = 125 GeV/c2. The production of neutral Higgs bosons in association with b-quarks can be significantly enhanced in various beyond the standard model scenarios, including Supersymmetry. The recent combination of such searches from the two collaborations is discussed.

    Jung Chang, Kingman Cheung, Po-Yan Tseng, Tzu-Chiang Yuan

    The new particle around 125 GeV observed at the LHC is almost consistent with the standard model Higgs boson, except that the diphoton decay mode may be excessive. We summarize a number of possibilities. We propose to use the vector-boson fusion to test the underlying model for electroweak symmetry breaking. Using the well known dijet-tagging technique to single out the vector-boson fusion mechanism, we investigate potential of vector-boson fusion to discriminate a number of models suggested to give an enhanced inclusive diphoton production rate.

    Pran Nath

    We review the recent discovery of the Higgs like particle at ~ 125 GeV and its implications for particle physics models. Specifically the implications of the relatively high Higgs mass for the discovery of supersymmetry are discussed. Several related topics such as naturalness and supersymmetry, dark matter and unification are also discussed.

    Shu-Wei Song, Lin Wen, Chao-Fei Liu, S.-C. Gou, Wu-Ming Liu

    We present an overview of our recent theoretical studies on the quantum phenomena of the spin-1 Bose–Einstein condensates, including the phase diagram, soliton solutions and the formation of the topological spin textures. A brief exploration of the effects of spin–orbit coupling on the ground-state properties is given.We put forward proposals by using the transmission spectra of an optical cavity to probe the quantum ground states: the ferromagnetic and polar phases. Quasi-one-dimension solitons and ring dark solitons are studied. It is predicted that characteristics of the magnetic solitons in optical lattice can be tuned by controlling the long-range light-induced and static magnetic dipoledipole interactions; solutions of single-component magnetic and single-, two-, three-components polar solitons are found; ring dark solitons in spin-1 condensates are predicted to live longer lifetimes than that in their scalar counterparts. In the formation of spin textures, we have considered the theoretical model of a rapidly quenched and fast rotating trapped spin-1 Bose–Einstein condensate, whose dynamics can be studied by solving the stochastic projected Gross–Pitaevskii equations. Spontaneous generation of nontrivial topological defects, such as the hexagonal lattice skyrmions and square lattice of half-quantized vortices was predicted. In particular, crystallization of merons (half skyrmions) can be generated in the presence of spin–orbit coupling.

    Yu-Ren Shi (石玉仁), Xue-Ling Wang (王雪玲), Guang-Hui Wang (王光辉), Cong-Bo Liu (刘丛波), Zhi-Gang Zhou (周志刚), Hong-Juan Yang(杨红娟)

    The homotopy analysis method and Galerkin spectral method are applied to find the analytical solutions for the Gross–Pitaevskii equations, a set of nonlinear Schr?dinger equation used in simulation of spin-1 Bose–Einstein condensates trapped in a harmonic potential. We investigate the one-dimensional case and get the approximate analytical solutions successfully. Comparisons between the analytical solutions and the numerical solutions have been made. The results indicate that they are in agreement well with each other when the atomic interaction is weakly. We also find a class of exact solutions for the stationary states of the spin-1 system with harmonic potential for a special case.

    Li-Sheng Geng

    Baryon chiral perturbation theory (BChPT), as an effective field theory of low-energy quantum chromodynamics (QCD), has played and is still playing an important role in our understanding of non-perturbative strong-interaction phenomena. In the past two decades, inspired by the rapid progress in lattice QCD simulations and the new experimental campaign to study the strangeness sector of low-energy QCD, many efforts have been made to develop a fully covariant BChPT and to test its validity in all scenarios. These new endeavours have not only deepened our understanding of some long-standing problems, such as the power-counting-breaking problem and the convergence problem, but also resulted in theoretical tools that can be confidently applied to make robust predictions Particularly, the manifestly covariant BChPT supplemented with the extended-on-mass-shell (EOMS) renormalization scheme has been shown to satisfy all analyticity and symmetry constraints and converge relatively faster compared to its non-relativistic and infrared counterparts. In this article, we provide a brief review of the fully covariant BChPT and its latest applications in the u, d, and s three-flavor sector.

    Zong-Qiang Yuan, Zhi-Gang Zheng

    The spatiotemporal propagation of a momentum excitation on the finite Fermi–Pasta–Ulam lattices is investigated. The competition between the solitary wave and phonons gives rise to interesting propagation behaviors. For a moderate nonlinearity, the initially excited pulse may propagate coherently along the lattice for a long time in a solitary wave manner accompanied by phonon tails. The lifetime of the long-transient propagation state exhibits a sensitivity to the nonlinear parameter. The solitary wave decays exponentially during the final loss of stability, and the decay rate varying with the nonlinear parameter exhibits two different scaling laws. This decay is found to be related to the largest Lyapunov exponent of the corresponding Hamiltonian system, which manifests a transition from weak to strong chaos. The mean-free-path of the solitary waves is estimated in the strong chaos regime, which may be helpful to understand the origin of anomalous conductivity in the Fermi–Pasta–Ulam lattice.