45,368 research outputs found

    A web-tool for population synthesis of near-by cooling neutron stars: An on-line test for cooling curves

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    We present a new web-tool - Net-PSICoNS - for population synthesis of isolated near-by cooling neutron stars (NSs). The main aim is to provide an easy test of models of the NS thermal evolution which can be used by groups studying this subject. A user can upload cooling curves for a set of masses, modify the mass spectrum if necessary, change radii to fit the EoS used for cooling curve calculations, and then a population synthesis of close-by isolated cooling NSs is performed. The output includes the Log N -- Log S distribution confronted with the ROSAT observations and several other sets of data. In this paper, we summarize the idea of the test proposed by Popov et al. (2006), and present a user's manual for the web-tool.Comment: 6 pages, accepted to A

    Holomorphic Analogs of Topological Gauge Theories

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    We introduce a new class of gauge field theories in any complex dimension, based on algebra-valued (p,q)-forms on complex n-manifolds. These theories are holomorphic analogs of the well-known Chern-Simons and BF topological theories defined on real manifolds. We introduce actions for different special holomorphic BF theories on complex, Kahler and Calabi-Yau manifolds and describe their gauge symmetries. Candidate observables, topological invariants and relations to integrable models are briefly discussed.Comment: 12 pages, LaTeX2e, shortened PLB versio

    Towards laser based improved experimental schemes for multiphoton e+ e- pair production from vacuum

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    Numerical estimates for pair production from vacuum in the presence of strong electromagnetic fields are derived, for two experimental schemes : the First concerns a laser based X-FEL and the other imitates the E144 experiment. The approximation adopted in this work is that of two level multiphoton on resonance. Utilizing achievable values of laser beam parameters, an enhancedproduction efficiency of up to 10^11 and 10^15 pairs can be obtained, for the two schemes respectively.Comment: 6 pages, 4 figure

    Symmetries in nonlinear Bethe-Heitler process

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    Nonlinear Bethe-Heitler process in a bichromatic laser field is investigated using strong-field QED formalism. Symmetry properties of angular distributions of created ee+e^-e^+ pairs are analyzed. These properties are showed to be governed by a behavior of the vector potential characterizing the laser field, rather than by the respective electric field component.Comment: 4 pages, 4 figure

    Closed N=2 Strings: Picture-Changing, Hidden Symmetries and SDG Hierarchy

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    We study the action of picture-changing and spectral flow operators on a ground ring of ghost number zero operators in the chiral BRST cohomology of the closed N=2 string and describe an infinite set of symmetry charges acting on physical states. The transformations of physical string states are compared with symmetries of self-dual gravity which is the effective field theory of the closed N=2 string. We derive all infinitesimal symmetries of the self-dual gravity equations in 2+2 dimensional spacetime and introduce an infinite hierarchy of commuting flows on the moduli space of self-dual metrics. The dependence on moduli parameters can be recovered by solving the equations of the SDG hierarchy associated with an infinite set of abelian symmetries generated recursively from translations. These non-local abelian symmetries are shown to coincide with the hidden abelian string symmetries responsible for the vanishing of most scattering amplitudes. Therefore, N=2 string theory "predicts" not only self-dual gravity but also the SDG hierarchy.Comment: 41 pages, no figure

    On a scale-invariant Fermi gas in a time-dependent harmonic potential

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    We investigate a scale-invariant two-component Fermi gas in a time-dependent isotropic harmonic potential. The exact time evolution of the density distribution in position space in any spatial dimension is obtained. Two experimentally relevant examples, an abrupt change and a periodic modulation of the trapping frequency are solved. Small deviations from scale invariance and isotropy of the confinement are addressed within first order perturbation theory. We discuss the consequences for experiments with ultracold quantum gases such as the excitation of a tower of undamped breathing modes and a new alternative for measuring the Tan contact.Comment: 6+3 pages, 2 figures; revised and extended versio

    Measurements of single top-quark production in pp collisions by the CMS experiment

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    A summary of studies of electroweak top-quark production performed by the CMS collaboration is presented. The results include measurements of production cross sections, extraction of the value of Vtb|V_{tb}|, determination of W-boson helicity in top-quark decays and top-quark spin asymmetry, and a search for anomalous couplings in the Wtb vertex. No deviations from predictions of the standard model are found.Comment: Proceedings of the 8th International Workshop on the CKM Unitarity Triangle (CKM 2014), Vienna, Austria, September 8-12, 201

    Identification of signal events in a search for HbbˉH\to b\bar b produced in association with single top quarks

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    The CMS collaboration has performed a search for an associated production of Higgs bosons and single top quarks in the HbbˉH\to b\bar b decay channel. The measurement is challenged by a complex multijet final state and an overwhelming background from top-quark pair production. These proceedings address a particular aspect of the search and describe the procedure deployed to discriminate the signal process from backgrounds.Comment: Presented at 7th international workshop on top quark physics (TOP2014); 4 pages, 3 figure