1,034 research outputs found

    Transport coefficients of a unitarized pion gas

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    The latest experimental results in relativistic heavy-ion collisions show that the matter there produced requires transport coefficients because of the important collective properties found. We review the theoretical calculation of these transport coefficients in the hadron side at low temperatures by computing them in a gas composed of low energy pions. The interaction of these pions is taken from an effective chiral theory and further requiring scattering unitarity. The propagation of D and D* mesons in the thermalized pion gas is also studied in order to extract the heavy quark diffusion coefficients in the system.Comment: 7 pages, 3 figures, contribution to the International School of Nuclear Physics, 33rd Course: From Quarks and Gluons to Hadrons and Nuclei, Erice-Sicily: 16-24 September 201

    On the Equivalence Theorem in the χPT\chi PT Description of the Symmetry Breaking Sector of the Standard Model

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    We develop an alternative formulation of the symmetry breaking sector of the Standard Model as a gauged non-linear sigma model (NLSM) following the philosophy of the Chiral lagrangian approach, which is the only compatible with all the experimental and theoretical constraints. We derive the BRS symmetry of the model and the corresponding quantum lagrangian, which is a generalization of the standard Faddeev-Popov method, in a way which is covariant with respect to the reparametrizations of the coset space of the NLSM. Then we use the BRS invariance of the quantum lagrangian to state the Equivalence Theorem for the renormalized SS-matrix elements calculated as a chiral expansion.Comment: LaTeX. Final version as it will appear in Nuclear Physics B (1994

    Brout-Englert-Higgs mechanism for accelerating observers

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    In this work we consider the spontaneous symmetry breaking of the electroweak SU(2)L×U(1)YSU(2)_L\times U(1)_Y gauge group into U(1)emU(1)_{em} taken place in the Standard Model of particle physics as seen from the point of view of an accelerating observer. According to the Unruh effect that observer detects the Minkowski vacuum as a thermal bath at a temperature proportional to the proper acceleration aa. Then we show that (in a certain large NN limit) when the acceleration is bigger than the critical value ac=4πva_c = 4 \pi v (where vv is the Higgs vacuum expectation value), the electroweak SU(2)L×U(1)YSU(2)_L\times U(1)_Y gauge symmetry is restored and all elementary particles become massless. In addition, even observers with a<aca<a_c, can see this symmetry restoration in the region close to the Rindler horizon

    Dark matter clues in the muon anomalous magnetic moment

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    We study the possibility to explain the non-baryonic dark matter abundance and improve the present fits on the muon anomalous magnetic moment through the same new physics. The only viable way to solve simultaneously both problems which is known to date is by using supersymmetric theories. However in this work we show that massive brane fluctuations (branons) in large extra-dimensions models can provide a more economical alternative to supersymmetry. This is so because the low-energy branon physics depends effectively on only three parameters. Next collider experiments, such as LHC or ILC, will be sensitive to branon phenomenology in the natural parameter region where the theory is able to account for the two effects.Comment: 4 pages, 3 figures, REVTeX

    The Equivalence Theorem for Chiral Lagrangians

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    In this work we derive the version of the Equivalence Theorem that applies when the symmetry breaking sector of the Standard Model is described by a general chiral lagrangian. The demonstration is valid for renormalized fields for any value of the gauge parameter (in RξR_{\xi} gauges) and any parametrization of the coset space. It is based in the absence of gauge anomalies which makes it possible to build an (anti)-BRS invariant chiral lagrangian in terms of the renormalized fields and therefore to use the corresponding Ward identities to obtain the theorem.Comment: 18 pages, LaTeX, FT/UCM/2/94 (We have corrected some errata

    Bulk viscosity of low-temperature strongly interacting matter

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    We study the bulk viscosity of a pion gas in unitarized Chiral Perturbation Theory at low and moderate temperatures, below any phase transition to a quark-gluon plasma phase. We argue that inelastic processes are irrelevant and exponentially suppressed at low temperatures. Since the system falls out of chemical equilibrium upon expansion,a pion chemical potential must be introduced, so we extend the existing theory to include it. We control the zero modes of the collision operator and Landau's conditions of fit when solving the Boltzmann equation with the elastic collision kernel. The dependence of the bulk viscosity with temperature is reminiscent of the findings of Fernandez-Fraile and Gomez Nicola, while the numerical value is closer to that of Davesne. In the zero-temperature limit we correctly recover the vanishing viscosity associated to a non-relativistic monoatomic gas.Comment: 8 pages, 8 figure

    Primordial torsion fields as an explanation of the anisotropy in cosmological electromagnetic propagation

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    In this note we provide a simple explanation of the recent finding of anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston (astro-ph/9704196). We consider, as a possible origin of such effect, the effective coupling between EM fields and some tiny background torsion field. The coupling is obtained after integrating out charged fermions, it is gauge invariant and does not require the introduction of any new physics.Comment: 8 pages, LaTeX, one figure, enlarged version with minor correction

    Study of gamma gamma -> W_L W_L and gamma gamma -> Z_L Z_L reactions with Chiral Lagrangians

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    We analyze the effects of a strongly interacting symmetry breaking sector of the Standard Model in γγ−>WL+WL−\gamma \gamma -> W_L^+ W_L^- and γγ−>ZLZL\gamma \gamma -> Z_L Z_L reactions at TeV energies by using Chiral Lagrangians and Chiral Perturbation Theory. We find significant deviations from the Standard Model predictions for the differential cross sections at high invariant mass of the gauge bosons pair. We study the experimental signals that could be obtained in a high energy and high luminosity dedicated γγ\gamma\gamma collider and estimate the sensitivity that such experiments could reach to the values of the effective lagrangian parameters.Comment: 14 pages, LaTeX, 4 figures (not included), FTUAM92/2
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