15,830 research outputs found
Coulomb Glasses: A Comparison Between Mean Field and Monte Carlo Results
Recently a local mean field theory for both eqilibrium and transport
properties of the Coulomb glass was proposed [A. Amir et al., Phys. Rev. B 77,
165207 (2008); 80, 245214 (2009)]. We compare the predictions of this theory to
the results of dynamic Monte Carlo simulations. In a thermal equilibrium state
we compare the density of states and the occupation probabilities. We also
study the transition rates between different states and find that the mean
field rates underestimate a certain class of important transitions. We propose
modified rates to be used in the mean field approach which take into account
correlations at the minimal level in the sense that transitions are only to
take place from an occupied to an empty site. We show that this modification
accounts for most of the difference between the mean field and Monte Carlo
rates. The linear response conductance is shown to exhibit the Efros-Shklovskii
behaviour in both the mean field and Monte Carlo approaches, but the mean field
method strongly underestimates the current at low temperatures. When using the
modified rates better agreement is achieved
Production of q bar-q Pairs in Proton-Nucleus Collisions at High Energies
We calculate production of quark-antiquark pairs in high energy
proton-nucleus collisions both in the quasi-classical approximation of
McLerran-Venugopalan model and including quantum small- evolution. The
resulting production cross section is explicitly expressed in terms of
Glauber-Mueller multiple rescatterings in the classical case and in terms of
dipole-nucleus scattering amplitude in the quantum evolution case. We
generalize the result of one of us (K.T.) beyond the aligned jet
configurations. We expand on the earlier results of Blaizot, Gelis and
Venugopalan by deriving quark production cross section including quantum
evolution corrections in rapidity intervals both between the quarks and the
target and between the quarks and the projectile.Comment: 18 pages, 3 figures; typos corrected, discussion extende
Coulomb gap in the one-particle density of states in three-dimensional systems with localized electrons
The one-particle density of states (1P-DOS) in a system with localized
electron states vanishes at the Fermi level due to the Coulomb interaction
between electrons. Derivation of the Coulomb gap uses stability criteria of the
ground state. The simplest criterion is based on the excitonic interaction of
an electron and a hole and leads to a quadratic 1P-DOS in the three-dimensional
(3D) case. In 3D, higher stability criteria, including two or more electrons,
were predicted to exponentially deplete the 1P-DOS at energies close enough to
the Fermi level. In this paper we show that there is a range of intermediate
energies where this depletion is strongly compensated by the excitonic
interaction between single-particle excitations, so that the crossover from
quadratic to exponential behavior of the 1P-DOS is retarded. This is one of the
reasons why such exponential depletion was never seen in computer simulations.Comment: 6 pages, 1 figur
Hadron multiplicity in pp and AA collisions at LHC from the Color Glass Condensate
We provide quantitative predictions for the rapidity, centrality and energy
dependencies of inclusive charged-hadron productions for the forthcoming LHC
measurements in nucleus-nucleus collisions based on the idea of gluon
saturation in the color-glass condensate framework. Our formulation gives very
good descriptions of the first data from the LHC for the inclusive
charged-hadron production in proton-proton collisions, the deep inelastic
scattering at HERA at small Bjorken-x, and the hadron multiplicities in
nucleus-nucleus collisions at RHIC.Comment: 7 pages, 8 figures; v3: minor changes, one reference added, results
unchanged, the version to appear in Phys. Rev.
Nucleation of Spontaneous Vortices in Trapped Fermi Gases Undergoing a BCS-BEC Crossover
We study the spontaneous formation of vortices during the superfluid
condensation in a trapped fermionic gas subjected to a rapid thermal quench via
evaporative cooling. Our work is based on the numerical solution of the time
dependent crossover Ginzburg-Landau equation coupled to the heat diffusion
equation. We quantify the evolution of condensate density and vortex length as
a function of a crossover phase parameter from BCS to BEC. The more interesting
phenomena occur somewhat nearer to the BEC regime and should be experimentally
observable; during the propagation of the cold front, the increase in
condensate density leads to the formation of supercurrents towards the center
of the condensate as well as possible condensate volume oscillations.Comment: 5 pages, 3 figure
Study of non-collinear parton dynamics in the prompt photon photoproduction at HERA
We investigate the prompt photon photoproduction at HERA within the framework
of kt-factorization QCD approach. Our consideration is based on the off-shell
matrix elements for the underlying partonic subprocesses. The unintegrated
parton densities in a proton and in a photon are determined using the
Kimber-Martin-Ryskin (KMR) prescription. Additionally, we use the CCFM-evolved
unintegrated gluon as well as valence and sea quark distributions in a proton.
A conservative error analisys is performed. Both inclusive and associated with
the hadronic jet production rates are investigated. The theoretical results are
compared with the recent experimental data taken by the H1 and ZEUS
collaborations. We study also the specific kinematical properties of the
photon-jet system which are strongly sensitive to the transverse momentum of
incoming partons. Using the KMR scheme, the contribution from the quarks
emerging from the earlier steps of the parton evolution is estimated and found
to be of 15 - 20 approximately.Comment: 22 pages, 13 figures, 2 tabl
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