442 research outputs found

    Gauge Couplings at High Temperature and the Relic Gravitino Abundance

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    In higher-dimensional supersymmetric theories gauge couplings of the effective four-dimensional theory are determined by expectation values of scalar fields. We find that at temperatures above a critical temperature T∗T_*, which depends on the supersymmetry breaking mass scales, gauge couplings decrease like T^{-\a}, \a > 1. This has important cosmological consequences. In particular it leads to a relic gravitino density which becomes independent of the reheating temperature for TR>T∗T_R > T_*. For small gravitino masses, m_{3/2} \ll m_{\gl}, the mass density of stable gravitinos is essentially determined by the gluino mass. The observed value of cold dark matter, \O_{\rm CDM}h^2 \sim 0.1, is obtained for gluino masses m_{\gl} = {\cal O}(1 {\rm TeV}).Comment: 11 pages, 2 figures, comment on supersymmetry breaking mechanisms and two references adde

    A note on the predictions of models with modular flavor symmetries

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    Models with modular flavor symmetries have been thought to be highly predictive. We point out that these predictions are subject to corrections from non–holomorphic terms in the Lagrangean. Specifically, in the models discussed in the literature, the Kähler potential is not fixed by the symmetries, for instance. The most general Kähler potential consistent with the symmetries of the model contains additional terms with additional parameters, which reduce the predictive power of these constructions. We also comment on potential ways of how one may conceivably retain the predictivity

    The Flavor of Cosmology

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    We discuss the cosmology of models in which the standard model Yukawa couplings depend on scalar field(s), often referred to as flavons. We find that thermal corrections of the flavon potential tend to decrease the Yukawa couplings, providing an important input to model-building. Working in the specific framework of Froggatt-Nielsen models, we compute the abundance of flavons in the early universe generated both via freeze-in and from coherent oscillations induced by thermal corrections to their potential, and discuss constraints on flavon models from cosmology. We find that cosmology places important constraints on theories containing flavons even for regions of parameter space inaccessible to collider searches.Comment: 26 pages, 5 figures, 5 appendice

    Gauged Discrete Symmetries and Proton Stability

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    We discuss the results of a search for anomaly free Abelian Z_N discrete symmetries that lead to automatic R-parity conservation and prevents dangerous higher-dimensional proton decay operators in simple extensions of the minimal supersymmetric extension of the standard model (MSSM) based on the left-right symmetric group, the Pati-Salam group and SO(10). We require that the superpotential for the models have enough structures to be able to give correct symmetry breaking to MSSM and potentially realistic fermion masses. We find viable models in each of the extensions and for all the cases, anomaly freedom of the discrete symmetry restricts the number of generations.Comment: 8 pages, 2 figures; v2 : typos fixed, references adde

    Non-thermal Gravitino Dark Matter in Gauge Mediation

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    We show that gravitinos produced by decays of a supersymmetry breaking scalar field (the pseudo-moduli field) can naturally explain the observed abundance of dark matter in a certain class of the gauge mediation models. We study the decay processes as well as cosmological constraints on this scenario in detail, particularly focusing on different behavior of the real and imaginary components of the pseudo-moduli field. Cosmologically viable scenario emerges when the gravitino and the pseudo-moduli masses are O(10-100) MeV and O(100) GeV, respectively.Comment: 32 pages, 10 figure

    Thermally induced subgap features in the cotunneling spectroscopy of a carbon nanotube

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    We report on nonlinear cotunneling spectroscopy of a carbon nanotube quantum dot coupled to Nb superconducting contacts. Our measurements show rich subgap features in the stability diagram which become more pronounced as the temperature is increased. Applying a transport theory based on the Liouville-von Neumann equation for the density matrix, we show that the transport properties can be attributed to processes involving sequential as well as elastic and inelastic cotunneling of quasiparticles thermally excited across the gap. In particular, we predict thermal replicas of the elastic and inelastic cotunneling peaks, in agreement with our experimental results.Comment: 21 pages, 9 figures, submitted to New Journal of Physic

    Asymptotic symmetries on Kerr--Newman horizon without anomaly of diffeomorphism invariance

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    We analyze asymptotic symmetries on the Killing horizon of the four-dimensional Kerr--Newman black hole. We first derive the asymptotic Killing vectors on the Killing horizon, which describe the asymptotic symmetries, and find that the general form of these asymptotic Killing vectors is the universal one possessed by arbitrary Killing horizons. We then construct the phase space associated with the asymptotic symmetries. It is shown that the phase space of an extreme black hole either has the size comparable with a non-extreme black hole, or is small enough to exclude degeneracy, depending on whether or not the global structure of a Killing horizon particular to an extreme black hole is respected. We also show that the central charge in the Poisson brackets algebra of these asymptotic symmetries vanishes, which implies that there is not an anomaly of diffeomorphism invariance. By taking into account other results in the literature, we argue that the vanishing central charge on a black hole horizon, in an effective theory, looks consistent with the thermal feature of a black hole. We furthermore argue that the vanishing central charge implies that there are infinitely many classical configurations that are associated with the same macroscopic state, while these configurations are distinguished physically.Comment: 14 pages, v2: references added, minor corrections, v3: new pars and refs. added and corresponding correction

    Clostridium difficile infection in the United States: A national study assessing preventive practices used and perceptions of practice evidence

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    We surveyed 571 US hospitals about practices used to prevent Clostridium difficile infection (CDI). Most hospitals reported regularly using key CDI prevention practices, and perceived their strength of evidence as high. The largest discrepancy between regular use and perceived evidence strength occurred with antimicrobial stewardship programs.Infect. Control Hosp. Epidemiol. 2015;36(8):969–971</jats:p
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