39,675 research outputs found
Sonine approximation for collisional moments of granular gases of inelastic rough spheres
We consider a dilute granular gas of hard spheres colliding inelastically
with coefficients of normal and tangential restitution and ,
respectively. The basic quantities characterizing the distribution function
of linear () and angular
() velocities are the second-degree moments defining the
translational () and rotational () temperatures. The
deviation of from the Maxwellian distribution parameterized by
and can be measured by the cumulants associated
with the fourth-degree velocity moments. The main objective of this paper is
the evaluation of the collisional rates of change of these second- and
fourth-degree moments by means of a Sonine approximation. The results are
subsequently applied to the computation of the temperature ratio
and the cumulants of two paradigmatic states: the
homogeneous cooling state and the homogeneous steady state driven by a
white-noise stochastic thermostat. It is found in both cases that the
Maxwellian approximation for the temperature ratio does not deviate much from
the Sonine prediction. On the other hand, non-Maxwellian properties measured by
the cumulants cannot be ignored, especially in the homogeneous cooling state
for medium and small roughness. In that state, moreover, the cumulant directly
related to the translational velocity differs in the quasi-smooth limit
from that of pure smooth spheres (). This singular
behavior is directly related to the unsteady character of the homogeneous
cooling state and thus it is absent in the stochastic thermostat case.Comment: 14 pages, 8 figures; v2: some parts rewritten, new references added;
published in a special topic decicated to Carlo Cercignan
Exclusive photoproduction of quarkonium in proton-nucleus collisions at energies available at the CERN Large Hadron Collider
In this work we investigate the coherent photoproduction of psi(1S), psi(2S)
and Upsilon (1S) states in the proton-nucleus collisions in the LHC energies.
Predictions for the rapidity distributions are presented using the color dipole
formalism and including saturation effects that are expected to be relevant at
high energies. Calculations are done at the energy 5.02 TeV and also for the
next LHC run at 8.8 TeV in proton-lead mode. Discussion is performed on the
main theoretical uncertainties associated to the calculations.Comment: 05 pages, 5 figures. Version to be published in Phys. Rev.
A New Form of Path Integral for the Coherent States Representation and its Semiclassical Limit
The overcompleteness of the coherent states basis leads to a multiplicity of
representations of Feynman's path integral. These different representations,
although equivalent quantum mechanically, lead to different semiclassical
limits. Two such semiclassical formulas were derived in \cite{Bar01} for the
two corresponding path integral forms suggested by Klauder and Skagerstan in
\cite{Klau85}. Each of these formulas involve trajectories governed by a
different classical representation of the Hamiltonian operator: the P
representation in one case and the Q representation in other. In this paper we
construct a third representation of the path integral whose semiclassical limit
involves directly the Weyl representation of the Hamiltonian operator, i.e.,
the classical Hamiltonian itself.Comment: 16 pages, no figure
Light vector meson photoproduction in hadron-hadron and nucleus-nucleus collisions at the energies available at the CERN Large Hadron Collider
In this work we analyse the theoretical uncertainties on the predictions for
the photoproduction of light vector mesons in coherent pp, pA and AA collisions
at the LHC energies using the color dipole approach. In particular, we present
our predictions for the rapidity distribution for rh0 and phi photoproduction
and perform an analysis on the uncertainties associated to the choice of vector
meson wavefunctionand the phenomenological models for the dipole cross section.
Comparison is done with the recent ALICE analysis on coherent production of rho
at 2.76 TeV in PbPb collisions.Comment: 07 pages, 6 figures. Version to be published in Phys. Rev.
Diffractive dissociation in proton-nucleus collisions at collider energies
The cross section for the nuclear diffractive dissociation in proton-lead
collisions at the LHC is estimated. Based on the current theoretical
uncertainties for the single (target) diffactive cross section in hadron-hadron
reactions one obtains sigma_SD(5.02 TeV) = 19.67 \pm 5.41 mb and sigma_SD(8.8
TeV) = 18.76 \pm 5.77 mb, respectively. The invariant mass M_X for the reaction
pPb -> pX is also analyzed. Discussion is performed on the main theoretical
uncertainties associated to the calculations.Comment: 04 pages, 2 figures. Final version to be published in European
Physical Journal A - "Hadrons and Nuclei
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