903 research outputs found

### Higher Twist Effects in Photon-Photon Collisions

In this article, we investigate the contribution of the high twist Feynman
diagrams to the large $p_{T}$ 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 $a_2$ and $a_4$
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 $\rho$-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 $p_{T}$ and the rapidity $y$ of meson in
$\Phi_{CLEO}(x,Q^2)$ wave function case is very close to the $\Phi_{asy}(x)$
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

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

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

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 $\epsilon_1 \mu_1=\epsilon_2\mu_2$. Upon deriving the general
expression for the Casimir energy, a dilute compact ball is considered
$(\epsilon_1 -\epsilon_2)^2/(\epsilon_1+\epsilon_2)^2\ll 1$. In this case the
calculations are carried out which are of the first order in $\xi ^2$ 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

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

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
$k$. Since current data indicate that the first derivative $\alpha_S$ of the
spectral index $n_S(k_0)$ is negative at the pivot scale $k_0$, PBH formation
is only possible in the presence of a sizable and positive second derivative
("running of the running") $\beta_S$. 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
$\alpha_S$, which is weakly preferred by current data.Comment: 26 pages, 5 figures, Refs. added, Minor textual change; version to
appear in JCA

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