84 research outputs found
Remarks on the Coulomb and Covariant Gauges in Finite Temperature QED
We compare the use of the Coulomb gauge in finite temperature QED with a
recently proposed prescription for covariant gauges, in which only the
transverse photon degrees of freedom are thermalized. Using the Landau rule as
a guide, we clarify the relation between the retarded electron self-energy and
the elements of the self-energy matrix in the real-time formulation of . The
general results are illustrated by means of the one-loop expressions for the
electron self-energy in a QED plasma.Comment: LaTeX, 10 pages, no figures; to be published in Phys. Lett.
The electromagnetic vertex of neutrinos in an electron background and a magnetic field
We study the electromagnetic vertex function of a neutrino that propagates in
an electron background in the presence of a static magnetic field. The
structure of the vertex function under the stated conditions is determined and
it is written down in terms of a minimal and complete set of tensors. The
one-loop expressions for all the form factors is given, up to terms that are
linear in the magnetic field, and the approximate integral formulas that hold
in the long wavelength limit are obtained. We discuss the physical
interpretation of some of the form factors and their relation with the concept
of the neutrino induced charge. The neutrino acquires a longitudinal and a
transverse charge, due to the fact that the form factors depend on the
transverse and longitudinal components of the photon momentum independently. We
compute those form factors explicitly in various limiting cases and find that
the longitudinal and transverse charge are the same for the case of a
non-relativistic electron gas, but not otherwise.Comment: 18 pages. Revtex4, axodra
Axial vector current in an electromagnetic field and low-energy neutrino-photon interactions
An expression for the axial vector current in a strong, slowly varying
electromagnetic field is obtained. We apply this expression to the construction
of the effective action for low-energy neutrino-photon interactions.Comment: 6 pages, references updated, final version to appear in Phys. Rev.
Weak and strong disjunction in possibilistic asp
Abstract. Possibilistic answer set programming (PASP) unites answer set programming (ASP) and possibilistic logic (PL) by associating certainty values with rules. The resulting framework allows to combine both non-monotonic reasoning and reasoning under uncertainty in a single framework. While PASP has been well-studied for possibilistic definite and possibilistic normal programs, we argue that the current semantics of possibilistic disjunctive programs are not entirely satisfactory. The problem is twofold. First, the treatment of negation-as-failure in existing approaches follows an all-or-nothing scheme that is hard to match with the graded notion of proof underlying PASP. Second, we advocate that the notion of disjunction can be interpreted in several ways. In particular, in addition to the view of ordinary ASP where disjunctions are used to induce a non-deterministic choice, the possibilistic setting naturally leads to a more epistemic view of disjunction. In this paper, we propose a semantics for possibilistic disjunctive programs, discussing both views on disjunction. Extending our earlier work, we interpret such programs as sets of constraints on possibility distributions, whose least specific solutions correspond to answer sets.
Plasma wave instabilities induced by neutrinos
Quantum field theory is applied to study the interaction of an electron
plasma with an intense neutrino flux. A connection is established between the
field theory results and classical kinetic theory. The dispersion relation and
damping rate of the plasma longitudinal waves are derived in the presence of
neutrinos. It is shown that Supernova neutrinos are never collimated enough to
cause non-linear effects associated with a neutrino resonance. They only induce
neutrino Landau damping, linearly proportional to the neutrino flux and
.Comment: 18 pages, 3 figures, title and references correcte
Chiral unitary approach to S-wave meson baryon scattering in the strangeness S=0 sector
We study the S-wave interaction of mesons with baryons in the strangeness S=0
sector in a coupled channel unitary approach. The basic dynamics is drawn from
the lowest order meson baryon chiral Lagrangians. Small modifications inspired
by models with explicit vector meson exchange in the t-channel are also
considered. In addition the pi pi N channel is included and shown to have an
important repercussion in the results, particularly in the isospin 3/2 sector.Comment: 23 pages, LaTeX, 21 figure
Neutrino damping rate at finite temperature and density
A first principle derivation is given of the neutrino damping rate in
real-time thermal field theory. Starting from the discontinuity of the neutrino
self energy at the two loop level, the damping rate can be expressed as
integrals over space phase of amplitudes squared, weighted with statistical
factors that account for the possibility of particle absorption or emission
from the medium. Specific results for a background composed of neutrinos,
leptons, protons and neutrons are given. Additionally, for the real part of the
dispersion relation we discuss the relation between the results obtained from
the thermal field theory, and those obtained by the thermal average of the
forward scattering amplitude.Comment: LaTex Document, 19 pages, 3 figure
Structure of the Quark Propagator at High Temperature
In the high temperature, chirally invariant phase of QCD, the quark
propagator is shown to have two sets of poles with different dispersion
relations. A reflection property in momentum space relates all derivatives at
zero-momentum of the particle and hole energies, the particle and hole damping
rates, and the particle and hole residues. No use is made of perturbation
theory.Comment: 8 pages, Latex twocolum
Chiral dynamics of p-wave in K^- p and coupled states
We perform an evaluation of the p-wave amplitudes of meson-baryon scattering
in the strangeness S=-1 sector starting from the lowest order chiral
Lagrangians and introducing explicitly the Sigma^* field with couplings to the
meson-baryon states obtained using SU(6) symmetry. The N/D method of
unitarization is used, equivalent, in practice, to the use of the
Bethe-Salpeter equation with a cut-off. The procedure leaves no freedom for the
p-waves once the s-waves are fixed and thus one obtains genuine predictions for
the p-wave scattering amplitudes, which are in good agreement with experimental
results for differential cross sections, as well as for the width and partial
decay widths of the Sigma^*(1385).Comment: LaTeX, 18 pages, 6 figure
On a Neutrino Electroweak Radius
We study a combination of amplitudes for neutrino scattering that can isolate
a (gauge-invariant) difference of chirality-preserving neutrino electroweak
radii for and . This involves both photon and
exchange contributions. It is shown that the construction singles out the
contributions of the hypercharge gauge field in the standard model.
We comment on how gauge-dependent terms from the charge radii cancel with other
terms in the relative electroweak radii defined.Comment: 16 pages, revtex with embedded figure
- …