13,411 research outputs found

    Discrimination of Σ\Sigma-nucleus potentials in the angular distribution of elastic scattering of Σ\Sigma^- hyperons from nuclei

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    We theoretically investigate the elastic scattering of 50-MeV Σ\Sigma^- hyperons from 28^{28}Si and 208^{208}Pb in order to clarify the radial distribution of Σ\Sigma-nucleus (optical) potentials. The angular distributions of differential cross sections are calculated using several potentials that can explain experimental data of the Σ\Sigma^- atomic X-ray and (π\pi^-, K+K^+) reaction spectra simultaneously. The magnitude and oscillation pattern of the angular distributions are understood by the use of nearside/farside decompositions of their scattering amplitudes. It is shown that the resultant angular distributions can considerably discriminate among the radial distributions of the potentials that have a repulsion inside the nuclear surface and an attraction outside the nucleus with a sizable absorption

    Heavy-light meson in anisotropic lattice QCD

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    We examine whether the O(a)O(a) improved quark action on anisotropic lattices can be used as a framework for the heavy quark, which enables precision computation of matrix elements of heavy-light mesons. To this end, it is crucial to verify that a mass independent and nonperturbative tuning of the parameters is possible. As a first step, we observe the dispersion relation of heavy-light mesons on a quenched lattice using the action which is nonperturbatively tuned only for the leading terms. On a lattice with the spatial cutoff aσ1a_\sigma^{-1} \simeq 1.6 GeV and the anisotropy ξ=4\xi=4, the relativity relation holds within 2% accuracy in the quark mass region aσmQ1.2a_\sigma m_Q \leq 1.2 with the bare anisotropy parameter tuned for the massless quark. We also apply the action to a calculation of heavy-light decay constants in the charm quark mass region.Comment: Lattice2002(heavyquark), 3 pages, 2 figure

    Newtonian Analysis of Gravitational Waves from Naked Singularity

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    Spherical dust collapse generally forms a shell focusing naked singularity at the symmetric center. This naked singularity is massless. Further the Newtonian gravitational potential and speed of the dust fluid elements are everywhere much smaller than unity until the central shell focusing naked singularity formation if an appropriate initial condition is set up. Although such a situation is highly relativistic, the analysis by the Newtonian approximation scheme is available even in the vicinity of the space-time singularity. This remarkable feature makes the analysis of such singularity formation very easy. We investigate non-spherical even-parity matter perturbations in this scheme by complementary using numerical and semi-analytical approaches, and estimate linear gravitational waves generated in the neighborhood of the naked singularity by the quadrupole formula. The result shows good agreement with the relativistic perturbation analysis recently performed by Iguchi et al. The energy flux of the gravitational waves is finite but the space-time curvature carried by them diverges.Comment: 23 pages, 8 figure

    A Reversibility Parameter for a Markovian Stepper

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    Recent experimental studies on the stepwize motion of biological molecular motors have revealed that the ``characteristic distance'' of a step is usually less than the actual step size. This observation implies that the detailed-balance condition for kinetic rates of steps is violated in these motors. In this letter, in order to clarify the significance of the characteristic distance, we study a Langevin model of a molecular motor with a hidden degree of freedom. We find that the ratio of the characteristic distance to the step size is equal to unity if the dominant paths in the state space are one dimensional, while it deviates from unity if the dominant paths are branched. Therefore, this parameter can be utilized to determine the reversibility of a motor even under a restricted observation.Comment: 6 pages, 2 figures - minor revision

    Analytic derivation of the map of null rays passing near a naked singularity

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    Recently the energy emission from a naked singularity forming in spherical dust collapse has been investigated. This radiation is due to the particle creation in a curved spacetime. In this discussion, the central role is played by the mapping formula between the incoming and the outgoing null coordinates. For the self-similar model, this mapping formula has been derived analytically. But for the model with CC^{\infty} density profile, the mapping formula has been obtained only numerically. In the present paper, we argue that the singular nature of the mapping is determined by the local geometry around the point at which the singularity is first formed. If this is the case, it would be natural to expect that the mapping formula can be derived analytically. In the present paper, we analytically rederive the same mapping formula for the model with CC^{\infty} density profile that has been earlier derived using a numerical technique.Comment: 4 pages, submitted to Phys. Rev.