2,101 research outputs found
Angular momentum non-conserving decays in isotropic media
Various processes that are forbidden in the vacuum due to angular momentum
conservation can occur in a medium that is isotropic and does not carry any
angular momentum. We illustrate this by considering explicitly two examples.
The first one is the decay of a spin-0 particle into a photon and another
spin-0 particle, using a model involving the Yukawa interactions of the scalar
particles with a charged fermion field. The second one involves the decay of a
neutrino into another neutrino and a graviton, in the standard model of
particle interactions augmented with the linearized gravitational couplings.Comment: 22 pages, Latex, uses axodraw.sty. 3 figures embedded in the tex
file. This paper contains the same material as that presented in two earlier
papers, arXiv:0901.2981 and arXiv:0901.2982, written by us. This version
supersedes those two paper
Non-universal gravitational couplings of neutrinos in matter
When neutrinos travel through a normal matter medium, the electron neutrinos
couple differently to gravity compared to the other neutrinos, due to the
presence of electrons in the medium and the absence of the other charged
leptons. The matter-induced gravitational couplings of the neutrinos under such
conditions are calculated and their contribution to the neutrino index of
refraction in the presence of a gravitational potential is determined.Comment: Latex, 10 page
Neutrino propagation in an electron background with an inhomogeneous magnetic field
We study the electromagnetic coupling of a neutrino that propagates in a
two-stream electron background medium. Specifically, we calculate the
electromagnetic vertex function for a medium that consists of a \emph{normal}
electron background plus another electron \emph{stream} background that is
moving with a velocity four-vector relative to the normal background.
The results can be used as the basis for studying the neutrino electromagnetic
properties and various processes in such a medium. As an application, we
calculate the neutrino dispersion relation in the presence of an external
magnetic field (), focused in the case in which is inhomogeneous,
keeping only the terms of the lowest order in and linear in the
and its gradient. We show that the dispersion relation contains additional
anisotropic terms involving the derivatives of , such as the gradient
of , which involve the stream background
velocity, and a term of the form that can be
present in the absence of the stream background, in addition to a term of the
form and the well known term that
arises in the constant case. The derivative-dependent terms are even
under a transformation. As a result, in contrast to the latter two just
mentioned, they depend on the sum of the particle and antiparticle densities
and therefore can be non-zero in a -symmetric medium in which the particle
and antiparticle densities are equal.Comment: Title changes, 39 pages, 2 figure
Thermal Field Theory in a wire: Applications of Thermal Field Theory methods to the propagation of photons in a one-dimensional plasma
We apply the Thermal Field Theory (TFT) methods to study the propagation of
photons in a plasma wire, that is, a system in which the electrons are confined
to a one-dimensional tube or wire, but are otherwise free. We find the
appropriate expression for the photon \emph{free-field} propagator in such a
medium, and write down the dispersion relation in terms of the free-field
propagator and the photon self-energy. The self-energy is then calculated in
the one-loop approximation and the corresponding dispersion relation is
determined and studied in some detail. Our work differs from previous work on
this subject in that we do not adopt any specific electronic wave functions in
the coordinates that are transverse to the idealized wire, or rely on
particular features of the electronic structure. We treat the electrons as a
free gas of particles, constrained to move in one dimension, but otherwise in a
model-independent way only following the rules of TFT adapted to the situation
at hand. For the appropriate conditions of the plasma the \emph{static
approximation} can be employed and the dispersion relation reduces to the
results obtained in previous works, but the formula that we obtain is valid
under more general conditions, including those in which the static
approximation is not valid. In particular, the dispersion relation has several
branches, which are not revealed if the static approximation is used. The
dispersion relations obtained reproduce several unique features of these
systems that have been observed in recent experiments.Comment: 17 pages Revised and extended discussion of the dispersion relation
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