631 research outputs found
Free energy for non-equilibrium quasi-stationary states
We study a class of non-equilibrium quasi-stationary states for a Markov
system interacting with two different thermal baths. We show that the work done
under a slow, external change of parameters admits a potential, i.e., the free
energy. Three conditions are needed for the existence of free energy in this
non-equilibrium system: time-scale separation between variables of the system,
partial controllability (external fields couple only with the slow variable),
and an effective detailed balance. These conditions are facilitated in the
continuous limit for the slow variable. In contrast to its equilibrium
counterpart, the non-equilibrium free energy can increase with temperature. One
example of this is that entropy reduction by means of external fields (cooling)
can be easier (in the sense of the work cost) if it starts from a higher
temperature.Comment: 8 pages, 2 figure
Production of Z^0 bosons with rapidity gaps: exclusive photoproduction in gamma p and p p collisions and inclusive double diffractive Z^0's
We extend the k_\perp-factorization formalism for exclusive photoproduction
of vector mesons to the production of electroweak Z^0 bosons. Predictions for
the gamma p \to Z^0 p and p p \to p p Z^0 reactions are given using an
unintegrated gluon distribution tested against deep inelastic data. We present
distributions in the Z^0 rapidity, transverse momentum of Z^0 as well as in
relative azimuthal angle between outgoing protons. The contributions of
different flavours are discussed. Absorption effects lower the cross section by
a factor of 1.5-2, depending on the Z-boson rapidity. We also discuss the
production of Z^0 bosons in central inclusive production. Here rapidity and
(x_{\Pom,1}, x_{\Pom,2}) distributions of Z^0 are calculated. The corresponding
cross section is about three orders of magnitude larger than that for the
purely exclusive process.Comment: 19 pages, 14 figs, A. Cisek is married name of A. Rybarsk
Particle spectrum in modified NMSSM
The restrictions on the lightest Higgs boson mass in the minimal
supersymmetric models are briefly reviewed. The particle spectrum is considered
in the framework of the simplest modification of NMSSM that allows to avoid the
domain wall problem and to get the self--consistent solution in the strong
Yukawa coupling limit. The lightest Higgs boson mass in the investigated model
can reach at values of and does not exceed
.Comment: 4 pages, LaTeX2e. Talk given at the SUSY 2001 Conference in JINR,
Dubna, Russi
Reactive self-heating model of aluminum spherical nanoparticles
Aluminum-oxygen reaction is important in many highly energetic, high pressure
generating systems. Recent experiments with nanostructured thermites suggest
that oxidation of aluminum nanoparticles occurs in a few microseconds. Such
rapid reaction cannot be explained by a conventional diffusion-based mechanism.
We present a rapid oxidation model of a spherical aluminum nanoparticle, using
Cabrera-Mott moving boundary mechanism, and taking self-heating into account.
In our model, electric potential solves the nonlinear Poisson equation. In
contrast with the Coulomb potential, a "double-layer" type solution for the
potential and self-heating leads to enhanced oxidation rates. At maximal
reaction temperature of 2000 C, our model predicts overall oxidation time scale
in microseconds range, in agreement with experimental evidence.Comment: submitte
Exclusive photoproduction of in proton-proton and proton-antiproton scattering
Protons and antiprotons at collider energies are a source of high energy
Weizs\"acker--Williams photons. This may open a possibility to study exclusive
photoproduction of heavy vector mesons at energies much larger than possible at
the HERA accelerator. Here we present a detailed investigation of the exclusive
photoproduction in proton-proton (RHIC, LHC) and proton-antiproton
(Tevatron) collisions. We calculate several differential distributions in , as well as transverse momentum distributions of 's. We
discuss correlations in the azimuthal angle between outgoing protons or proton
and antiproton as well as in the () space. Differently from
electroproduction experiments, here both colliding beam particles can be a
source of photons, and we find large interference terms in azimuthal angle
distributions in a broad range of rapidities of the produced meson. We also
include the spin--flip parts in the electromagnetic vertices. We discuss the
effect of absorptive corrections on various distributions. Interestingly,
absorption corrections induce a charge asymmetry in rapidity distributions, and
are larger for reactions than for the case. The reaction
considered here constitutes an important nonreduceable background in recently
proposed searches for odderon exchange.Comment: 22 pages, 20 figures; dedicated to Kolya Nikolaev on the occasion of
his 60th birthday; 4 figures and discussion adde
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