903 research outputs found

    Higher Twist Effects in Photon-Photon Collisions

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    In this article, we investigate the contribution of the high twist Feynman diagrams to the large pTp_{T} single pseudoscalar and vector mesons inclusive production cross section in two-photon collisions and we present the general formulae for the high and leading twist differential cross sections. The pion wave function where two non-trivial Gegenbauer coefficients a2a_2 and a4a_4 have been extracted from the CLEO data, Braun-Filyanov pion wave function, the asymptotic and the Chernyak-Zhitnitsky wave functions are used in the calculations. For ρ\rho-meson we used Ball-Braun wave function. The results of all the calculations reveal that the high twist cross sections, the ratio R, the dependence transverse momentum pTp_{T} and the rapidity yy of meson in ΦCLEO(x,Q2)\Phi_{CLEO}(x,Q^2) wave function case is very close to the Φasy(x)\Phi_{asy}(x) asymptotic wave function case. It is shown that the high twist contribution to the cross section depends on the choice of the meson wave functions.Comment: REVTEX4, 23 pages, 7 figure

    Division Forms Development and Control

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    A. Columbus City Code mandates that all new forms have a retention schedule established within one year of creation or receipt. B. The policies and procedures set forth in this Directive apply to both paper and electronic forms

    Non-extremal Localised Branes and Vacuum Solutions in M-Theory

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    Non-extremal overlapping p-brane supergravity solutions localised in their relative transverse coordinates are constructed. The construction uses an algebraic method of solving the bosonic equations of motion. It is shown that these non-extremal solutions can be obtained from the extremal solutions by means of the superposition of two deformation functions defined by vacuum solutions of M-theory. Vacuum solutions of M-theory including irrational powers of harmonic functions are discussed.Comment: LaTeX, 16 pages, no figures, typos correcte

    Direct mode summation for the Casimir energy of a solid ball

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    The Casimir energy of a solid ball placed in an infinite medium is calculated by a direct frequency summation using the contour integration. It is assumed that the permittivity and permeability of the ball and medium satisfy the condition ϵ1μ1=ϵ2μ2\epsilon_1 \mu_1=\epsilon_2\mu_2. Upon deriving the general expression for the Casimir energy, a dilute compact ball is considered (ϵ1ϵ2)2/(ϵ1+ϵ2)21(\epsilon_1 -\epsilon_2)^2/(\epsilon_1+\epsilon_2)^2\ll 1. In this case the calculations are carried out which are of the first order in ξ2\xi ^2 and take account of the five terms in the Debye expansion of the Bessel functions involved. The implication of the obtained results to the attempts of explaining the sonoluminescence via the Casimir effect is shortly discussed.Comment: REVTeX, 7 pages, no figures and tables, treatment of a dilute dielectric ball is revised, new references are adde

    Stress and Strain in Flat Piling of Disks

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    We have created a flat piling of disks in a numerical experiment using the Distinct Element Method (DEM) by depositing them under gravity. In the resulting pile, we then measured increments in stress and strain that were associated with a small decrease in gravity. We first describe the stress in terms of the strain using isotropic elasticity theory. Then, from a micro-mechanical view point, we calculate the relation between the stress and strain using the mean strain assumption. We compare the predicted values of Young's modulus and Poisson's ratio with those that were measured in the numerical experiment.Comment: 9 pages, 1 table, 8 figures, and 2 pages for captions of figure

    Running Spectral Index and Formation of Primordial Black Hole in Single Field Inflation Models

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    A broad range of single field models of inflation are analyzed in light of all relevant recent cosmological data, checking whether they can lead to the formation of long-lived Primordial Black Holes (PBHs). To that end we calculate the spectral index of the power spectrum of primordial perturbations as well as its first and second derivatives. PBH formation is possible only if the spectral index increases significantly at small scales, i.e. large wave number kk. Since current data indicate that the first derivative αS\alpha_S of the spectral index nS(k0)n_S(k_0) is negative at the pivot scale k0k_0, PBH formation is only possible in the presence of a sizable and positive second derivative ("running of the running") βS\beta_S. Among the three small-field and five large-field models we analyze, only one small-field model, the "running mass" model, allows PBH formation, for a narrow range of parameters. We also note that none of the models we analyze can accord for a large and negative value of αS\alpha_S, which is weakly preferred by current data.Comment: 26 pages, 5 figures, Refs. added, Minor textual change; version to appear in JCA