2,479 research outputs found
On geometric relativistic foundations of matter field equations and plane wave solutions
In this paper, we start from the geometric relativistic foundations to define
the basis upon which matter field theories are built, and their wave solutions
are investigated, finding that they display repulsive interactions able to
reproduce the exclusion principle in terms of its effects in a dynamical way,
then discussing possible consequences and problems.Comment: 11 page
Single Leptoquark Production at and Colliders
We consider single production of leptoquarks (LQ's) at and
colliders, for two values of the centre-of-mass energy,
GeV and 1 TeV. We find that LQ's which couple within the first
generation are observable for LQ masses almost up to the kinematic limit, both
at and colliders, for the LQ coupling strength equal to
. The cross sections for single production of - and
-generation LQ's at colliders are too small to be observable.
In collisions, on the other hand, -generation LQ's with
masses much larger than can be detected. However,
-generation LQ's can be seen at colliders only for
masses at most , making their observation more probable via the
pair production mechanism.Comment: plain TeX, 14 pages, 6 figures (not included but available on
request), some minor changes to the text, one reference added, figures and
conclusions unchanged, UdeM-LPN-TH-93-152, McGill-93/2
Field-dependent diamagnetic transition in magnetic superconductor
The magnetic penetration depth of single crystal
was measured down to 0.4 K in dc fields up
to 7 kOe. For insulating , Sm spins order at the
N\'{e}el temperature, K, independent of the applied field.
Superconducting ( K) shows a
sharp increase in diamagnetic screening below which varied from
4.0 K () to 0.5 K ( 7 kOe) for a field along the c-axis. If the
field was aligned parallel to the conducting planes, remained
unchanged. The unusual field dependence of indicates a spin freezing
transition that dramatically increases the superfluid density.Comment: 4 pages, RevTex
On details of the thermodynamical derivation of the Ginsburg--Landau equations
We examine the procedure of thermodynamical derivation of the
Ginsburg--Landau equation for current, which is given unclear and contradictory
interpretations in existing textbooks. We clarify all steps of this procedure
and find as a consequence a limitation on the validity range of the
thermodynamic Ginsburg--Landau theory, which does not seem to be explicitely
stated up to now: we conclude that the thermodynamic theory is applicable only
to a superconducting specimen that is not a part of an external
current-carrying loop.Comment: 11 pages. Accepted for publication in 'Superconductor Science and
Technology
Effective Potential for Scalar Field in Three Dimensions: Ising Model in the Ferromagnetic Phase
We compute the effective potential for one-component real
scalar field in three Euclidean dimensions (3D) in the case of
spontaneously broken symmetry, from the Monte Carlo simulation of the 3D Ising
model in external field at temperatures approaching the phase transition from
below. We study probability distributions of the order parameter on the
lattices from to , at . We find that, in close
analogy with the symmetric case, plays an important role: is very well approximated by the sum of , and
terms. An unexpected feature is the negative sign of the
term. As close to the continuum limit as we can get (), we
obtain
We also compute several universal coupling constants and ratios, including
the combination of critical amplitudes .Comment: 13 pages, 5 Postscript figures, uses epsf.st
Resistivity study of the pseudogap phase for (Hg,Re) - 1223 superconductors
The pseudogap phase above the critical temperature of high
superconductors (HTSC) presents different energy scales and it is currently a
matter of intense study. The complexity of the HTSC normal state requires very
accurate measurements with the purpose of distinguishing different types of
phenomena. Here we have performed systematically studies through electrical
resistivity () measurements by several different current densities in
order to obtain an optimal current for each sample. This approach allows to
determine reliable values of the pseudogap temperature , the layer
coupling temperature between the superconductor layers , the
fluctuation temperature and the critical temperature as
function of the doping . The interpretation of these different temperature
scales allows to characterize possible scenarios for the (Hg,Re) - 1223 normal
state. This method, described in detail here, and used to derive the
(Hg,Re)-1223 phase diagram is general and can be applied to any HTSC.Comment: 31 pages, 12 figures, Latex; 25 pages, LaTeX; 11 figures; rewrited
section II and III; added 18 reference; rewrited title, added discussion
sectio
Fields of accelerated sources: Born in de Sitter
This paper deals thoroughly with the scalar and electromagnetic fields of
uniformly accelerated charges in de Sitter spacetime. It gives details and
makes various extensions of our Physical Review Letter from 2002. The basic
properties of the classical Born solutions representing two uniformly
accelerated charges in flat spacetime are first summarized. The worldlines of
uniformly accelerated particles in de Sitter universe are defined and described
in a number of coordinate frames, some of them being of cosmological
significance, the other are tied naturally to the particles. The scalar and
electromagnetic fields due to the accelerated charges are constructed by using
conformal relations between Minkowski and de Sitter space. The properties of
the generalized `cosmological' Born solutions are analyzed and elucidated in
various coordinate systems. In particular, a limiting procedure is demonstrated
which brings the cosmological Born fields in de Sitter space back to the
classical Born solutions in Minkowski space. In an extensive Appendix, which
can be used independently of the main text, nine families of coordinate systems
in de Sitter spacetime are described analytically and illustrated graphically
in a number of conformal diagrams.Comment: 37 pages, 23 figures, reformatted version of the paper published in
JMP; low-resolution figures due to arXiv size restrictions; for the version
with high-resolution figures see http://utf.mff.cuni.cz/~krtous/papers
Observation of a New Mechanism of Spontaneous Generation of Magnetic Flux in a Superconductor
We report the discovery of a new mechanism of spontaneous generation of a
magnetic flux in a superconductor cooled through . The sign of the
spontaneous flux changes randomly from one cooldown to the next, and follows a
Gaussian distribution. The width of the distribution increases with the size of
the temperature gradient in the sample. Our observations appear inconsistent
with the well known mechanisms of flux generation. The dependence on the
temperature gradient suggests that the flux may be generated through an
instability of the thermoelectric superconducting-normal quasiparticle
counterflow
Melting of a p-H2 monolayer on a lithium substrate
Adsorption of para-hydrogen films on Alkali metals substrates at low
temperature is studied theoretically by means of Path Integral Monte Carlo
simulations. Realistic potentials are utilized to model the interaction between
two para-hydrogen molecules, as well as between a para-hydrogenmolecule and the
substrate, assumed smooth. Results show that adsorption of para-hydrogen on a
Lithium substrate, the most attractive among the Alkali, occurs through
completion of successive solid adlayers. Each layer has a two-dimensional
density approximatley equal 0.070 inverse square Angstroms. A solid
para-hydrogen monolayer displays a higher degree of confinement, in the
direction perpendicular to the substrate, than a monolayer Helium film, and has
a melting temperature of about 6.5 K. The other Alkali substrates are not
attractive enough to be wetted by molecular hydrogen at low temperature. No
evidence of a possible superfluid phase of para-hydrogen is seen in these
systems.Comment: Scales on the y-axis in Figs. 4,5 and 7 are off by a factor 2 in
published version; corrected her
The dependence of the hard diffractive photoproduction of vector meson or photon and the range of pQCD validity
We consider two coupled problems.
We study the dependence on photon virtuality for the semihard
quasi--elastic photoproduction of neutral vector mesons on a quark, gluon or
real photon (at
GeV)). To this end we calculate the corresponding amplitudes (in an
analytical form) in the lowest nontrivial approximation of perturbative QCD. It
is shown that the amplitude for the production of light meson varies very
rapidly with the photon virtuality near .
We estimate the bound of the pQCD validity region for such processes. For the
real incident photon the obtained bound for the meson production is very
high. This bound decreases fast with the increase of , and we expect that
the virtual photoproduction at HERA gives opportunity to test the pQCD results.
The signature of this region is discussed. For the hard Compton effect the pQCD
should work good at not too high , and this effect seems measurable
at HERA.Comment: ReVTeX, 36 pages, 5 Postscript figures, uses epsf.st
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