280 research outputs found
Axion Emission from Red Giants and White Dwarfs
Using thermal field theory methods, we recalculate axion emission from dense
plasmas. We study in particular the Primakoff and the bremsstrahlung processes.
The Primakoff rate is significantly suppressed at high densities, when the
electrons become relativistic. However, the bound on the axion-photon coupling,
GeV, is unaffected, as it is constrained by the evolution of HB
stars, which have low densities. In contradistinction, the same relativistic
effects enhance the bremsstrahlung processes. From the red giants and white
dwarfs evolution, we obtain a conservative bound on the axion-electron
coupling, .Comment: 17 pp, 3 PS figures, CERN-TH-7044/9
Photon Propagation in Dense Media
Using thermal field theory, we derive simple analytic expressions for the
spectral density of photons in degenerate QED plasmas, without assuming the
usual non or ultra-relativistic limit. We recover the standard results in both
cases. Although very similar in ultra-relativistic plasmas, transverse and
longitudinal excitations behave very differently as the electron Fermi momentum
decreases.Comment: 12pp (3 PS figures available upon request), ENSLAPP-A-412/9
Resummation of Perturbation Series in Non-Equilibrium Scalar Field Theory
The general behaviour of perturbation series in non-equilibrium scalar field
theory is analysed in some detail, with a particular emphasis on the
``pathological terms'', generated by multiple products of -functions.
Using an intuitive regularization method, it is shown that these terms give
large contributions at all orders, even when considering small deviations from
equilibrium. Fortunately, these terms can also be resummed and I give the
general expressions for the resummed propagators in non-equilibrium scalar
field theory, regardless of the size of deviations from equilibrium.Comment: 11pp, 4 figures (uuencoded file), preprint CERN-TH.7336/9
Thermal quark production in ultra-relativistic nuclear collisions
We calculate thermal production of u, d, s, c and b quarks in
ultra-relativistic heavy ion collisions. The following processes are taken into
account: thermal gluon decay (g to ibar i), gluon fusion (g g to ibar i), and
quark-antiquark annihilation (jbar j to ibar i), where i and j represent quark
species. We use the thermal quark masses, ,
in all the rates. At small mass (), the production is largely
dominated by the thermal gluon decay channel. We obtain numerical and analytic
solutions of one-dimensional hydrodynamic expansion of an initially pure glue
plasma. Our results show that even in a quite optimistic scenario, all quarks
are far from chemical equilibrium throughout the expansion. Thermal production
of light quarks (u, d and s) is nearly independent of species. Heavy quark (c
and b) production is quite independent of the transition temperature and could
serve as a very good probe of the initial temperature. Thermal quark production
measurements could also be used to determine the gluon damping rate, or
equivalently the magnetic mass.Comment: 14 pages (latex) plus 6 figures (uuencoded postscript files);
CERN-TH.7038/9
Structure Functions of the Nucleon in a Statistical Model
Deep inelastic scattering is considered in a statistical model of the
nucleon. This incorporates certain features which are absent in the standard
parton model such as quantum statistical correlations which play a role in the
propagation of particles when considering Feynman diagrams containing internal
lines. The inclusion of the corrections in our numerical
calculations allows a good fit to the data for . The fit
corresponds to values of temperature and chemical potential of approximately
GeV and GeV. The latter values of parameters, however,
give rise, for all , to a large value for .Comment: 16 pages TeX, 11 figures available as Postscript files, University of
Bielefeld preprint BI-TP 93/3
Finite Temperature Renormalization of the - and -Models at Zero Momentum
A self-consistent renormalization scheme at finite temperature and zero
momentum is used together with the finite temperature renormalization group to
study the temperature dependence of the mass and the coupling to one-loop order
in the - and -models. It is found that the critical
temperature is shifted relative to the naive one-loop result and the coupling
constants at the critical temperature get large corrections. In the high
temperature limit of the \phiff-model the coupling decreases.Comment: 16 pages, plain Latex, NORDITA-92/38
Two Loop Low Temperature Corrections to Electron Self Energy
We recalculate the two loop corrections in the background heat bath using
real time formalism. The procedure of the integrations of loop momenta with
dependence on finite temperature before the momenta without it, has been
followed. We determine the mass and wavefunction renormalization constants in
the low temperature limit of QED, for the first time with this preferred order
of integrations. The correction to electron mass and spinors in this limit is
important in the early universe at the time of primordial nucleosynthesis as
well as in astrophysics.Comment: 8 pages and 1 figure to appear in Chinese Physics
Gap equation in scalar field theory at finite temperature
We investigate the two-loop gap equation for the thermal mass of hot massless
theory and find that the gap equation itself has a non-zero finite
imaginary part. This indicates that it is not possible to find the real thermal
mass as a solution of the gap equation beyond order in perturbation
theory. We have solved the gap equation and obtain the real and the imaginary
part of the thermal mass which are correct up to order in perturbation
theory.Comment: 13 pages, Latex with axodraw, Minor corrections, Appendix adde
The Electric Charge of Neutrinos and Plasmon Decay
By using both thermal field theory and a somewhat more intuitive method, we
define the electric charge as well as the charge radius of neutrinos
propagating inside a plasma. We show that electron neutrinos acquire a charge
radius of order cm, regardless of the properties of
the medium. Then, we compute the rate of plasmon decay which such an electric
charge or a charge radius implies. Taking into account the relativistic effects
of the degenerate electron gas, we compare our results to various
approximations as well as to recent calculations and determine the regimes
where the electric charge or the charge radius does mediate the decay of
plasmons. Finally, we discuss the stellar limits on any anomalous charge radius
of neutrinos.Comment: 19pp, 4 figures (available upon request), CERN-TH-7076/9
Comments on two papers by Kapusta and Wong
We critically examine recently published results on the thermal production of
massive vector bosons in a quark-gluon plasma. We claim the production rate is
a collinear safe observable.Comment: 6 pages LATEX documen
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