1,867 research outputs found
Saturation effects in exclusive rhoT, rhoL meson electroproduction
We use recent results for the gamma*L -> rhoL and gamma*T -> rhoT impact
factors, computed in the impact parameter representation within the collinear
factorization scheme, to get predictions for the polarized cross-sections
sigmaT and sigmaL of the diffractive leptoproduction of the rho meson at high
energy. In this approach the helicity amplitude is a convolution of the
scattering amplitude of a color dipole with a target, together with the virtual
gamma wave function and with the first moments of the rho meson wave function
(in the transverse momentum space), given by the distribution amplitudes up to
twist 3 for the gamma*T -> rhoT impact factor and up to twist 2 for the gamma*L
-> rhoL impact factor. Combining these results with recent dipole models fitted
to DIS data, which include saturation effects, we show that the predictions are
in good agreement with HERA data for photon virtuality (Q**2) larger than
typically 5 GeV**2, without free parameters and with a weak dependence on the
choice of the factorization scale, i.e. the shape of the DAs, for both
longitudinally and transversely polarized rho meson. For lower values of Q**2,
the inclusion of saturation effects is not enough to provide a good description
of HERA data. We believe that it is a signal of a need for higher twist
contributions in the rho meson DAs. We also analyze the radial distributions of
dipoles between the initial gamma* and the final rho meson states.Comment: 49 pages, 20 figure
Phenomenology of the polarized cross-sections of the rho meson leptoproduction at high energy
We present a model for the polarized cross-sections of the hard diffractive
leptoproduction of rho meson in the high energy limit. Our model is based on
the light-cone collinear factorization of the virtual photon to rho meson
impact factor when using the impact factor representation of the helicity
amplitudes of the rho meson leptoproduction. This gauge invariant treatment
when expressed in impact parameter space, leads to the factorization on one
hand of the color dipole scattering amplitude and on the other hand of the
distribution amplitudes of the rho meson up to twist 2 and 3. We show that the
results of this approach are in good agreement with HERA data for virtualities
above ~5 GeV^2.Comment: 6 pages, 3 figures, proceedings of Photon 2013, May 20 - 24 2013,
Paris, Franc
A model for high energy rho meson leptoproduction based on collinear factorization and dipole models
We present a phenomenological model for the helicity amplitudes T11 and T00
of the rho meson exclusive diffractive leptoproduction in the forward limit.
This model leads to a very good description of the polarized cross-sections
sigmaT and sigmaL when compared to HERA data. This model is based on the impact
factor representation of the helicity amplitudes. The gamma* -> rho impact
factor is computed within the light-cone collinear factorization scheme, the
impact parameter space representation allowing to factorize out the
dipole-target amplitude. Finally our description combines a model for the
dipole-target amplitude that includes the saturation effects with the results
for the impact factor where the twist 2 and twist 3 distribution amplitudes of
the rho meson are involved.Comment: 5 pages, 3 figures, to appear in the proceedings of XXI International
Workshop on Deep-Inelastic Scattering and Related Subject - DIS 2013, 22-26
April 2013, Marseille, Franc
High energy rho meson leptoproduction
We investigate the longitudinal and transverse polarized cross-sections of
the leptoproduction of the rho meson in the high energy limit. Our model is
based on the computation of the impact factor gamma*(lambda_gamma) ->
rho(lambda_rho) using the twist expansion in the forward limit and expressed in
the impact parameter space. This treatment involves in the final stage the
twist 2 and twist 3 distribution amplitudes (DAs) of the rho meson and the
dipole scattering amplitude. Taking models that exist for the DAs and for the
dipole cross-section, we get a phenomenological model for the helicity
amplitudes, we compare our predictions with HERA data and get a fairly good
description for large enough virtualities of the photon.Comment: 6 pages, 3 figures, proceedings of the International Workshop on Low
X Physics, May 30 - June 4 2013, Rehovot and Eilat, Israe
New string vacua from twistor spaces
We find a new family of AdS_4 vacua in IIA string theory. The internal space
is topologically either the complex projective space CP^3 or the "flag
manifold" SU(3)/(U(1)xU(1)), but the metric is in general neither Einstein nor
Kaehler. All known moduli are stabilized by fluxes, without using quantum
effects or orientifold planes. The analysis is completely ten--dimensional and
does not rely on assumptions about Kaluza--Klein reduction.Comment: 19 pages. v3: published version, further minor correction
Stochastic and deterministic models for age-structured populations with genetically variable traits
Understanding how stochastic and non-linear deterministic processes interact
is a major challenge in population dynamics theory. After a short review, we
introduce a stochastic individual-centered particle model to describe the
evolution in continuous time of a population with (continuous) age and trait
structures. The individuals reproduce asexually, age, interact and die. The
'trait' is an individual heritable property (d-dimensional vector) that may
influence birth and death rates and interactions between individuals, and vary
by mutation. In a large population limit, the random process converges to the
solution of a Gurtin-McCamy type PDE. We show that the random model has a long
time behavior that differs from its deterministic limit. However, the results
on the limiting PDE and large deviation techniques \textit{\`a la}
Freidlin-Wentzell provide estimates of the extinction time and a better
understanding of the long time behavior of the stochastic process. This has
applications to the theory of adaptive dynamics used in evolutionary biology.
We present simulations for two biological problems involving life-history trait
evolution when body size is plastic and individual growth is taken into
account.Comment: This work is a proceeding of the CANUM 2008 conferenc
A numerical approach for modelling thin cracked plates with XFEM
The modelization of bending plates with through the thickness cracks is investigated. We consider the Kirchhoff-Love plate model which is valid for very thin plates. We apply the eXtended Finite Element Method (XFEM) strategy: enrichment of the finite element space with the asymptotic bending and with the discontinuity across the crack. We present two variants and their numerical validations and also a numerical computation of the stress intensity factors
High Energy exclusive Leptoproduction of the rho-meson: Theory and Phenomenology
We describe the hard leptoproduction of transversally polarized rho-meson, up
to twist 3 accuracy, including 2- and 3- particles Fock-states, in the HERA
kinematics of high center-of-mass energy. We first build a model based on a
simple approach to the unintegrated gluon density (the parton impact factor)
that we compare with H1 and ZEUS data for the ratios of helicity amplitudes
T(gamma*T -> rhoT)/T(gamma*L -> rhoL) and T(gamma*T -> rhoL)/T(gamma*L -> rhoL)
and get a good description of the data. We also show how saturation effects can
be included in this model by extending the dipole representation of the
scattering amplitude in coordinate space up to twist 3.Comment: 4 pages, 3 figures, to appear in the proceedings of 20th
International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS
2012), Bonn, Germany, 26-30 March 201
Theory and phenomenology of helicity amplitudes for high energy exclusive leptoproduction of the rho-meson
We review here two approaches to describe hard leptoproduction of
transversally polarized rho-meson, based on recent calculation of the gamma*T
-> rhoT impact factor up to twist 3 accuracy in the collinear factorization
frame, including 2- and 3- particles Fock-states. The first approach uses a
model of the unintegrated gluon density (the proton impact factor) which allows
a comparison of our predictions with H1 and ZEUS data for the ratios of
helicity amplitudes T(gamma*T -> rhoT)/T(gamma*L -> rhoL) and T(gamma*T ->
rhoL)/T(gamma*L -> rhoL). In the second approach, we transform the gamma*T ->
rhoT impact factor into the impact parameter space. We show that the
transformed amplitude factorizes according to conventional dipole picture. We
shortly discuss a way to implement the nucleon saturation effects in our
approach.Comment: 5 pages, 2 figures, to appear in the proceedings of 6th International
Conference on Quarks and Nuclear Physics (QNP 2012), Palaiseau, France, April
16-20, 201
A phenomenological study of helicity amplitudes of high energy exclusive leptoproduction of the rho meson
We apply a previously developed scheme to consistently include the twist-3
distribution amplitudes for transversely polarized rho meson in order to
evaluate, in the framework of kT factorization, the helicity amplitudes for
exclusive leptoproduction of a light vector meson, at leading order in alphaS.
We compare our results with high energy experimental data for the ratios of
helicity amplitudes T11/T00 and T01/T00 and get a good description of the data.Comment: 20 pages, 11 figures, published version in PR
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