381 research outputs found

    Symmetry Nonrestoration at High Temperature in Little Higgs Models

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    A detailed study of the high temperature dynamics of the scalar sector of Little Higgs scenarios, proposed to stabilize the electroweak scale, shows that the electroweak gauge symmetry remains broken even at temperatures much larger than the electroweak scale. Although we give explicit results for a particular modification of the Littlest Higgs model, we expect that the main features are generic. As a spin-off, we introduce a novel way of dealing with scalar fluctuations in nonlinear sigma models, which might be of interest for phenomenological applications.Comment: 23 pages, LaTeX, 4 figure

    Soliton solutions of the improved quark mass density-dependent model at finite temperature

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    The improved quark mass density-dependent model (IQMDD) based on soliton bag model is studied at finite temperature. Appling the finite temperature field theory, the effective potential of the IQMDD model and the bag constant B(T)B(T) have been calculated at different temperatures. It is shown that there is a critical temperature TC110MeVT_{C}\simeq 110 \mathrm{MeV}. We also calculate the soliton solutions of the IQMDD model at finite tmperature. It turns out that when T<TCT<T_{C}, there is a bag constant B(T)B(T) and the soliton solutions are stable. However, when T>TCT>T_{C} the bag constant B(T)=0B(T)=0 and there is no soliton solution, therefore, the confinement of quarks are removed quickly.Comment: 10 pages, 9 figures; Version to appear in Physical Review

    1/N Expansion in Correlated Graphene

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    We examine the 1/N expansion, where N is the number of two-component Dirac fermions, for Coulomb interactions in graphene with a gap of magnitude Δ=2m\Delta = 2 m. We find that for Nα1N\alpha\gg1, where α\alpha is graphene's "fine structure constant", there is a crossover as a function of distance rr from the usual 3D Coulomb law, V(r)1/rV(r) \sim 1/r, to a 2D Coulomb interaction, V(r)ln(Nα/mr)V(r) \sim \ln(N\alpha/mr), for m1rm1Nα/6m^{-1} \ll r \ll m^{-1} N \alpha/6. This effect reflects the weak "confinement" of the electric field in the graphene plane. The crossover also leads to unusual renormalization of the quasiparticle velocity and gap at low momenta. We also discuss the differences between the interaction potential in gapped graphene and usual QED for different coupling regimes.Comment: 7 pages, 2 figures; expanded presentation, references adde

    Extended Thomas-Fermi Density Functional for the Unitary Fermi Gas

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    We determine the energy density ξ(3/5)nϵF\xi (3/5) n \epsilon_F and the gradient correction λ2(n)2/(8mn)\lambda \hbar^2(\nabla n)^2/(8m n) of the extended Thomas-Fermi (ETF) density functional, where nn is number density and ϵF\epsilon_F is Fermi energy, for a trapped two-components Fermi gas with infinite scattering length (unitary Fermi gas) on the basis of recent diffusion Monte Carlo (DMC) calculations [Phys. Rev. Lett. {\bf 99}, 233201 (2007)]. In particular we find that ξ=0.455\xi=0.455 and λ=0.13\lambda=0.13 give the best fit of the DMC data with an even number NN of particles. We also study the odd-even splitting γN1/9ω\gamma N^{1/9} \hbar \omega of the ground-state energy for the unitary gas in a harmonic trap of frequency ω\omega determining the constant γ\gamma. Finally we investigate the effect of the gradient term in the time-dependent ETF model by introducing generalized Galilei-invariant hydrodynamics equations.Comment: 7 pages, 3 figures, 1 table; corrected some typos; published in Phys. Rev. A; added erratum: see also the unpublished diploma thesis of Marco Manzoni (supervisors: N. Manini and L. Salasnich) at http://www.mi.infm.it/manini/theses/manzoni.pd

    Higgs Self-Coupling as a Probe of Electroweak Phase Transition

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    We argue that, within a broad class of extensions of the Standard Model, there is a tight corellation between the dynamics of the electroweak phase transition and the cubic self-coupling of the Higgs boson: Models which exhibit a strong first-order EWPT predict a large deviation of the Higgs self-coupling from the Standard Model prediction, as long as no accidental cancellations occur. Order-one deviations are typical. This shift would be observable at the Large Hadron Collider if the proposed luminosity or energy upgrades are realized, as well as at a future electron-positron collider such as the proposed International Linear Collider. These measurements would provide a laboratory test of the dynamics of the electroweak phase transition.Comment: 20 pages, 6 figures; minor changes to clarify a few point

    Vector order parameter in general relativity. Covariant equations

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    Phase transitions with spontaneous symmetry breaking and vector order parameter are considered in multidimensional theory of general relativity. Covariant equations, describing the gravitational properties of topological defects, are derived. The topological defects are classified in accordance with the symmetry of the covariant derivative of the vector order parameter. The abilities of the derived equations are demonstrated in application to the brane world concept. New solutions of the Einstein equations with a transverse vector order parameter are presented. In the vicinity of phase transition the solutions are found analytically

    Three-dimensional Roton-Excitations and Supersolid formation in Rydberg-excited Bose-Einstein Condensates

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    We study the behavior of a Bose-Einstein condensate in which atoms are weakly coupled to a highly excited Rydberg state. Since the latter have very strong van der Waals interactions, this coupling induces effective, nonlocal interactions between the dressed ground state atoms, which, opposed to dipolar interactions, are isotropically repulsive. Yet, one finds partial attraction in momentum space, giving rise to a roton-maxon excitation spectrum and a transition to a supersolid state in three-dimensional condensates. A detailed analysis of decoherence and loss mechanisms suggests that these phenomena are observable with current experimental capabilities.Comment: 4 pages, 5 figure