40,516 research outputs found

    Study of semileptonic and nonleptonic decays of the Bc−B_c^- meson

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    We evaluate semileptonic and two--meson nonleptonic decays of the Bc−B_c^- meson in the framework of a nonrelativistic quark model. The former are done in spectator approximation using one--body current operators at the quark level. Our model reproduces the constraints of heavy quark spin symmetry obtained in the limit of infinite heavy quark mass. For the two--meson nonleptonic decays we work in factorization approximation. We compare our results to the ones obtained in different relativistic approaches.Comment: Talk given at the IVth International Conference on Quarks an Nuclear Physics, Madrid, June 5th-10th 200

    Electromagnetic radiation produced by avalanches in the magnetization reversal of Mn12-Acetate

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    Electromagnetic radiation produced by avalanches in the magnetization reversal of Mn12-Acetate has been measured. Short bursts of radiation have been detected, with intensity significantly exceeding the intensity of the black-body radiation from the sample. The model based upon superradiance from inversely populated spin levels has been suggested

    Quantum dynamics of vortices in mesoscopic magnetic disks

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    Model of quantum depinning of magnetic vortex cores from line defects in a disk geometry and under the application of an in-plane magnetic field has been developed within the framework of the Caldeira-Leggett theory. The corresponding instanton solutions are computed for several values of the magnetic field. Expressions for the crossover temperature Tc and for the depinning rate \Gamma(T) are obtained. Fitting of the theory parameters to experimental data is also presented.Comment: 8 page

    Quark model study of the semileptonic B -> pi decay

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    The semileptonic decay B->pi is studied starting from a simple quark model and taking into account the effect of the B* resonance. A novel, multiply subtracted, Omn\`es dispersion relation has been implemented to extend the predictions of the quark model to all physical q^2 values. We find |V_{ub}|=0.0034 +/- 0.0003(exp.)+/- 0.0007(theory), in good agreement with experiment.Comment: Three pages, two figures. To appear in the proceedings of Quark Confinament and Hadron Spectrum VII. Azores, September 200

    Transverse parton momenta in single inclusive hadron production in e+e−{e^ + }{e^ - } annihilation processes

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    We study the transverse momentum distributions of single inclusive hadron production in e+e−{e^ + }{e^ - } annihilation processes. Although the only available experimental data are scarce and quite old, we find that the fundamental features of transverse momentum dependent (TMD) evolution, historically addressed in Drell-Yan processes and, more recently, in Semi-inclusive deep inelastic scattering processes, are visible in e+e−{e^ + }{e^ - } annihilations as well. Interesting effects related to its non-perturbative regime can be observed. We test two different parameterizations for the p⊥p_\perp dependence of the cross section: the usual Gaussian distribution and a power-law model. We find the latter to be more appropriate in describing this particular set of experimental data, over a relatively large range of p⊥p_\perp values. We use this model to map some of the features of the data within the framework of TMD evolution, and discuss the caveats of this and other possible interpretations, related to the one-dimensional nature of the available experimental data

    On the Jacobi-Metric Stability Criterion

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    We investigate the exact relation existing between the stability equation for the solutions of a mechanical system and the geodesic deviation equation of the associated geodesic problem in the Jacobi metric constructed via the Maupertuis-Jacobi Principle. We conclude that the dynamical and geometrical approaches to the stability/instability problem are not equivalent.Comment: 14 pages, no figure
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