168 research outputs found
Plasma influence on the neutrino - electron processes in a strong magnetic field
An influence of the magnetized electron - positron plasma on the absorption
and loss of the energy and momentum in a process of neutrino propagation is
investigated. A total contribution of all crossed processes, , , , , is
found for the first time, which appears not to depend on the chemical potential
of electron-positron gas. Relatively simple expressions for the probability and
mean losses of the neutrino energy and momentum are obtained, which are
suitable for a quantitative analysis.Comment: 8 pages, 1 ps figure, LaTeX, uses espcrc2.sty,epsf.sty, based on the
talks presented at the Xth International Baksan School "Particles and
Cosmology", Baksan Valley, Kabardino Balkaria, Russia, April 19-25, 1999 and
the International Workshop "Particles in Astrophysics and Cosmology: From
Theory to Observation", Valencia, Spain, May 3-8, 199
Gauge Invariant Variational Approach with Fermions: the Schwinger Model
We extend the gauge invariant variational approach of Phys. Rev. D52 (1995)
3719, hep-th/9408081, to theories with fermions. As the simplest example we
consider the massless Schwinger model in 1+1 dimensions. We show that in this
solvable model the simple variational calculation gives exact results.Comment: 14 pages, 1 figur
Influence of nonlocal electrodynamics on the anisotropic vortex pinning in
We have studied the pinning force density Fp of YNi_2B_2C superconductors for
various field orientations. We observe anisotropies both between the c-axis and
the basal plane and within the plane, that cannot be explained by usual mass
anisotropy. For magnetic field , the reorientation structural
transition in the vortex lattice due to nonlocality, which occurs at a field
, manifests itself as a kink in Fp(H). When , Fp is
much larger and has a quite different H dependence, indicating that other
pinning mechanisms are present. In this case the signature of nonlocal effects
is the presence of a fourfold periodicity of Fp within the basal plane.Comment: 4 pages, 3 figure
Large closed queueing networks in semi-Markov environment and its application
The paper studies closed queueing networks containing a server station and
client stations. The server station is an infinite server queueing system,
and client stations are single-server queueing systems with autonomous service,
i.e. every client station serves customers (units) only at random instants
generated by a strictly stationary and ergodic sequence of random variables.
The total number of units in the network is . The expected times between
departures in client stations are . After a service completion
in the server station, a unit is transmitted to the th client station with
probability , and being processed in the th client
station, the unit returns to the server station. The network is assumed to be
in a semi-Markov environment. A semi-Markov environment is defined by a finite
or countable infinite Markov chain and by sequences of independent and
identically distributed random variables. Then the routing probabilities
and transmission rates (which are expressed via
parameters of the network) depend on a Markov state of the environment. The
paper studies the queue-length processes in client stations of this network and
is aimed to the analysis of performance measures associated with this network.
The questions risen in this paper have immediate relation to quality control of
complex telecommunication networks, and the obtained results are expected to
lead to the solutions to many practical problems of this area of research.Comment: 35 pages, 1 figure, 12pt, accepted: Acta Appl. Mat
Neutrino-electron processes in a dense magnetized plasma
The neutrino-electron scattering in a dense degenerate magnetized plasma
under the conditions is investigated.
The volume density of the neutrino energy and momentum losses due to this
process are calculated. The results we have obtained demonstrate that plasma in
the presence of an external magnetic field is more transparent for neutrino
than non-magnetized plasma. It is shown that neutrino scattering under
conditions considered does not lead to the neutrino force acting on plasma.Comment: 11 pages, LATEX, to be published in Central European Science Journa
Macroscopic anisotropy in superconductors with anisotropic gaps
It is shown within the weak-coupling model that the macroscopic
superconducting anisotropy for materials with the gap varying on the Fermi
surface cannot be characterized by a single number, unlike the case of clean
materials with isotropic gaps. For clean uniaxial materials, the anisotropy
parameter defined as the ratio of London penetration depths,
, is evaluated for all 's. Within the two-gap model
of MgB, is an increasing function of .Comment: 4 pages, 2 figure
Confinement-Deconfinement Transition in 3-Dimensional QED
We argue that, at finite temperature, parity invariant non-compact
electrodynamics with massive electrons in 2+1 dimensions can exist in both
confined and deconfined phases. We show that an order parameter for the
confinement-deconfinement phase transition is the Polyakov loop operator whose
average measures the free energy of a test charge that is not an integral
multiple of the electron charge. The effective field theory for the Polyakov
loop operator is a 2-dimensional Euclidean scalar field theory with a global
discrete symmetry , the additive group of the integers. We argue that the
realization of this symmetry governs confinement and that the
confinement-deconfinement phase transition is of
Berezinskii-Kosterlitz-Thouless type. We compute the effective action to
one-loop order and argue that when the electron mass is much greater than
the temperature and dimensional coupling , the effective field theory
is the Sine-Gordon model. In this limit, we estimate the critical temperature,
.Comment: 11 pages, latex, no figure
Ballistic electron motion in a random magnetic field
Using a new scheme of the derivation of the non-linear -model we
consider the electron motion in a random magnetic field (RMF) in two
dimensions. The derivation is based on writing quasiclassical equations and
representing their solutions in terms of a functional integral over
supermatrices with the constraint . Contrary to the standard scheme,
neither singling out slow modes nor saddle-point approximation are used. The
-model obtained is applicable at the length scale down to the electron
wavelength. We show that this model differs from the model with a random
potential (RP).However, after averaging over fluctuations in the Lyapunov
region the standard -model is obtained leading to the conventional
localization behavior.Comment: 10 pages, no figures, to be submitted in PRB v2: Section IV is
remove
Upper critical field in dirty two-band superconductors: breakdown of the anisotropic Ginzburg-Landau theory
We investigate the upper critical field in a dirty two-band superconductor
within quasiclassical Usadel equations. The regime of very high anisotropy in
the quasi-2D band, relevant for MgB, is considered. We show that strong
disparities in pairing interactions and diffusion constant anisotropies for two
bands influence the in-plane in a different way at high and low
temperatures. This causes temperature-dependent anisotropy, in
accordance with recent experimental data in MgB. The three-dimensional
band most strongly influences the in-plane near , in the
Ginzburg-Landau (GL) region. However, due to a very large difference between
the c-axis coherence lengths in the two bands, the GL theory is applicable only
in an extremely narrow temperature range near . The angular dependence of
deviates from a simple effective-mass law even near .Comment: 12 pages, 5 figures, submitted to Phys.Rev.
Counting Domain Walls in N=1 Super Yang-Mills Theory
We study the multiplicity of BPS domain walls in N=1 super Yang-Mills theory,
by passing to a weakly coupled Higgs phase through the addition of fundamental
matter. The number of domain walls connecting two specified vacuum states is
then determined via the Witten index of the induced worldvolume theory, which
is invariant under the deformation to the Higgs phase. The worldvolume theory
is a sigma model with a Grassmanian target space which arises as the coset
associated with the global symmetries broken by the wall solution. Imposing a
suitable infrared regulator, the result is found to agree with recent work of
Acharya and Vafa in which the walls were realized as wrapped D4-branes in IIA
string theory.Comment: 28 pages, RevTeX, 3 figures; v2: discussion of the index slightly
expanded, using an alternative regulator, and references added; v3: typos
corrected, to appear in Phys. Rev.
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