57,127 research outputs found
Coupled fermion and boson production in a strong background mean-field
We derive quantum kinetic equations for fermion and boson production starting
from a phi^4 Lagrangian with minimal coupling to fermions. Decomposing the
scalar field into a mean-field part and fluctuations we obtain spontaneous pair
creation driven by a self-interacting strong background field. The produced
fermion and boson pairs are self-consistently coupled. Consequently back
reactions arise from fermion and boson currents determining the time dependent
self-interacting background mean-field. We explore the numerical solution in
flux tube geometry for the time evolution of the mean-field as well as for the
number- and energy densities for fermions and bosons. We find that after a
characteristic time all energy is converted from the background mean-field to
particle creation. Applying this general approach to the production of
``quarks'' and ``gluons'' a typical time scale for the collapse of the flux
tube is 1.5 fm/c.Comment: 9 pages, latex, epsfig, 7 figure
Geometry-induced localization of thermal fluctuations in ultrathin superconducting structures
Thermal fluctuations of the order parameter in an ultrathin triangular shaped
superconducting structure are studied near , in zero applied field. We
find that the order parameter is prone to much larger fluctuations in the
corners of the structure as compared to its interior. This geometry-induced
localization of thermal fluctuations is attributed to the fact that condensate
confinement in the corners is characterised by a lower effective
dimensionality, which favors stronger fluctuations.Comment: 9 pages, 5 figure
Dispersion of longitudinal momentum distributions induced in fragmentation reactions
On the basis of systematic measurements of fragmentation reactions, which
provide a detailed overview on the velocity distributions of residual nuclei,
an improved description of the kinematical properties of the fragmentation
residues is established. This work is dedicated to the fluctuations of their
momentum distributions. In contrast to previous investigations, limited to
close-to-projectile fragments, we extended our study to the entire production
range, down to the lightest observed fragments. In this context, beside the
contribution of abrasion and evaporation processes, we considered the effect of
the thermal break-up on the width of the momentum distributions. Using
approximated theoretical descriptions of the different reaction stages, a new
analytical formula for the variance of the momentum distribution is derived,
which is well adapted to technical applications.Comment: 14 pages, 3 figures, background info. at
http://www-wnt.gsi.de/charms
On a Possibility to Measure Thermoelectric Power in SNS Structures
Two dissimilar Josephson junctions, which are connected to a heater can act
as precise batteries. Because of the difference in thermoelectric power of
these batteries, circuit with two dissimilar batteries, under heat flow would have a net EMF around the zero-resistance
loop leading to a loop's magnetic flux oscillating in time. It is shown its
theoretical value is proportional to both the temperature difference as well as
the disparity in the thermoelectric powers of the two junctions.Comment: 5 page
Tuning orbital-selective correlation effects in superconducting RbFeSeS
We report on terahertz time-domain spectroscopy on superconducting and
metallic iron chalcogenides RbFeSeS. The
superconducting transition is reduced from 32 K () to 22 K
(), and finally suppressed () by isoelectronic substitution of Se
with S. Dielectric constant and optical conductivity exhibit a
metal-to-insulator transition associated with an orbital-selective Mott phase.
This orbital-selective Mott transition appears at higher temperature
with increasing sulfur content, identifying sulfur substitution as an efficient
parameter to tune orbital-dependent correlation effects in iron-chalcogenide
superconductors. The reduced correlations of the charge carriers can
account for the suppression of the superconductivity and the pseudogap-like
feature between and that was observed for .Comment: 6 pages, 4 figure
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