934 research outputs found
Stars and statistical physics: a teaching experience
The physics of stars, their workings and their evolution, is a goldmine of
problems in statistical mechanics and thermodynamics. We discuss many examples
that illustrate the possibility of deepening student's knowledge of statistical
mechanics by an introductory study of stars. The matter constituting the
various stellar objects provides examples of equations of state for classical
or quantal and relativistic or non-relativistic gases. Maximum entropy can be
used to characterize thermodynamic and gravitational equilibrium which
determines the structure of stars and predicts their instability above a
certain mass. Contraction accompanying radiation induces either heating or
cooling, which explains the formation of stars above a minimum mass. The
characteristics of the emitted light are understood from black-body radiation
and more precisely from the Boltzmann-Lorentz kinetic equation for photons. The
luminosity is governed by the transport of heat by photons from the center to
the surface. Heat production by thermonuclear fusion is determined by
microscopic balance equations. The stability of the steady state of stars is
controlled by the interplay of thermodynamics and gravitation.Comment: latex gould_last.tex, 4 files, submitted to Am. J. Phy
Non Perturbative Renormalization Group, momentum dependence of -point functions and the transition temperature of the weakly interacting Bose gas
We propose a new approximation scheme to solve the Non Perturbative
Renormalization Group equations and obtain the full momentum dependence of
-point functions. This scheme involves an iteration procedure built on an
extension of the Local Potential Approximation commonly used within the Non
Perturbative Renormalization Group. Perturbative and scaling regimes are
accurately reproduced. The method is applied to the calculation of the shift
in the transition temperature of the weakly repulsive Bose gas, a
quantity which is very sensitive to all momenta intermediate between these two
regions. The leading order result is in agreement with lattice calculations,
albeit with a theoretical uncertainty of about 25%. The next-to-leading order
differs by about 10% from the best accepted result
Proton-nucleus collisions in the color glass condensate framework
We discuss proton-nucleus collisions in the framework of the color glass
condensate. By assuming that the proton can be described as a low density color
source, we solve exactly the Yang-Mills equations corresponding to this type of
collision, and then use this solution in order to calculate inclusive gluon
production or quark-antiquark production. Our result shows that
k_T-factorization, while valid for gluon production, is violated for quark pair
production in proton-nucleus collisions.Comment: Talk given at SEWM2004, Helsinki, June 200
Non-Perturbative Renormalization Group calculation of the scalar self-energy
We present the first numerical application of a method that we have recently
proposed to solve the Non Perturbative Renormalization Group equations and
obtain the n-point functions for arbitrary external momenta. This method leads
to flow equations for the n-point functions which are also differential
equations with respect to a constant background field. This makes them, a
priori, difficult to solve. However, we demonstrate in this paper that, within
a simple approximation which turns out to be quite accurate, the solution of
these flow equations is not more complicated than that of the flow equations
obtained in the derivative expansion. Thus, with a numerical effort comparable
to that involved in the derivative expansion, we can get the full momentum
dependence of the n-point functions. The method is applied, in its leading
order, to the calculation of the self-energy in a 3-dimensional scalar field
theory, at criticality. Accurate results are obtained over the entire range of
momenta.Comment: 29 page
Violation of kT factorization in quark production from the Color Glass Condensate
We examine the violation of the kT factorization approximation for quark
production in high energy proton-nucleus collisions. We comment on its
implications for the open charm and quarkonium production in collider
experiments.Comment: 4 pages, 6 figures, contribution to proceedings of Quark Matter 2005,
Budapest, Aug 4-
Bulk and Edge excitations in a quantum Hall ferromagnet
In this article, we shall focus on the collective dynamics of the fermions in
a quantum Hall droplet. Specifically, we propose to look at the
quantum Hall ferromagnet. In this system, the electron spins are ordered in the
ground state due to the exchange part of the Coulomb interaction and the Pauli
exclusion principle. The low energy excitations are ferromagnetic magnons. To
provide a means for describing these magnons, we shall discuss a method of
introducing collective coordinates in the Hilbert space of many-fermion
systems. These collective coordinates are bosonic in nature. They map a part of
the fermionic Hilbert space into a bosonic Hilbert space. Using this technique,
we shall interpret the magnons as bosonic collective ex citations in the
Hilbert space of the many-electron Hall system. By considering a Hall droplet
of finite extent, we shall also obtain the effective Lagrangian governing the
spin collective excitations at the edge of the sample.Comment: Plain TeX 18 Pages Proceedings for the Y2K conference on strongly c
orrelated fermionic systems, Calcutta, Indi
Finite-temperature trapped dipolar Bose gas
We develop a finite temperature Hartree theory for the trapped dipolar Bose
gas. We use this theory to study thermal effects on the mechanical stability of
the system and density oscillating condensate states. We present results for
the stability phase diagram as a function of temperature and aspect ratio. In
oblate traps above the critical temperature for condensation we find that the
Hartree theory predicts significant stability enhancement over the
semiclassical result. Below the critical temperature we find that thermal
effects are well described by accounting for the thermal depletion of the
condensate. Our results also show that density oscillating condensate states
occur over a range of interaction strengths that broadens with increasing
temperature.Comment: 10 pages, 7 figure
Gluon Quasiparticles and the Polyakov Loop
A synthesis of Polyakov loop models of the deconfinement transition and
quasiparticle models of gluon plasma thermodynamics leads to a class of models
in which gluon quasiparticles move in a non-trivial Polyakov loop background.
These models are successful candidates for explaining both critical behavior
and the equation of state for the SU(3) gauge theory at temperatures above the
deconfinement temperature T_c. Polyakov loops effects are most important at
intermediate temperatures from T_c up to roughly 2.5 T_c, while quasiparticle
mass effects provide the dominant correction to blackbody behavior at higher
temperatures.Comment: 6 pages, 7 eps figures, revtex
Exotic spin, charge and pairing correlations of the two-dimensional doped Hubbard model: a symmetry entangled mean-field approach
Intertwining of spin, charge and pairing correlations in the repulsive
two-dimensional Hubbard model is shown through unrestricted variational
calculations, with projected wavefunctions free of symmetry breaking. A
crossover from incommensurate antiferromagnetism to stripe order naturally
emerges in the hole-doped region when increasing the on-site coupling. Although
effective pairing interactions are identified, they are strongly fragmented in
several modes including d-wave pairing and more exotic channels related to an
underlying stripe. We demonstrate that the entanglement of a mean-field
wavefunction by symmetry restoration can largely account for interaction
effects.Comment: Minor corrections, one reference adde
Exact Calculation of Ring Diagrams and the Off-shell Effect on the Equation of State
The partition function with ring diagrams at finite temperature is exactly
caluclated by using contour integrals in the complex energy plane. It contains
a pole part with temperature and momentum dependent mass and a phase shift part
induced by off-shell effect in hot medium. The thermodynamic potentials for
and interactions are calculated and compared with the
quasi-particle (pole) approximation. It is found that the off-shell effect on
the equation of state is remarkable.Comment: 7 pages, 11 figures, refereces added, final version to appear in PR
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