1,165 research outputs found
Chiral Symmetry Restoration and Deconfinement to Quark Matter in Neutron Stars
We describe an extension of the hadronic SU(3) non-linear sigma model to
include quarks. As a result, we obtain an effective model which interpolates
between hadronic and quark degrees of freedom. The new parameters and the
potential for the Polyakov loop (used as the order parameter for deconfinement)
are calibrated in order to fit lattice QCD data and reproduce the QCD phase
diagram. Finally, the equation of state provided by the model, combined with
gravity through the inclusion of general relativity, is used to make
predictions for neutron stars.Comment: Prepared for Light-Cone 2009, Sao Jose dos Campos, Brazil, 8-13 July
2009
-Spectral theory of locally symmetric spaces with -rank one
We study the -spectrum of the Laplace-Beltrami operator on certain
complete locally symmetric spaces with finite volume and
arithmetic fundamental group whose universal covering is a
symmetric space of non-compact type. We also show, how the obtained results for
locally symmetric spaces can be generalized to manifolds with cusps of rank
one
Enhanced stability of the square lattice of a classical bilayer Wigner crystal
The stability and melting transition of a single layer and a bilayer crystal
consisting of charged particles interacting through a Coulomb or a screened
Coulomb potential is studied using the Monte-Carlo technique. A new melting
criterion is formulated which we show to be universal for bilayer as well as
for single layer crystals in the case of (screened) Coulomb, Lennard--Jones and
1/r^{12} repulsive inter-particle interactions. The melting temperature for the
five different lattice structures of the bilayer Wigner crystal is obtained,
and a phase diagram is constructed as a function of the interlayer distance. We
found the surprising result that the square lattice has a substantial larger
melting temperature as compared to the other lattice structures. This is a
consequence of the specific topology of the defects which are created with
increasing temperature and which have a larger energy as compared to the
defects in e.g. a hexagonal lattice.Comment: Accepted for publication in Physical Review
Current-induced highly dissipative domains in high Tc thin films
We have investigated the resistive response of high Tc thin films submitted
to a high density of current. For this purpose, current pulses were applied
into bridges made of Nd(1.15)Ba(1.85)Cu3O7 and Bi2Sr2CaCu2O8. By recording the
time dependent voltage, we observe that at a certain critical current j*, a
highly dissipative domain develops somewhere along the bridge. The successive
formation of these domains produces stepped I-V characteristics. We present
evidences that these domains are not regions with a temperature above Tc, as
for hot spots. In fact this phenomenon appears to be analog to the nucleation
of phase-slip centers observed in conventional superconductors near Tc, but
here in contrast they appear in a wide temperature range. Under some
conditions, these domains will propagate and destroy the superconductivity
within the whole sample. We have measured the temperature dependence of j* and
found a similar behavior in the two investigated compounds. This temperature
dependence is just the one expected for the depairing current, but the
amplitude is about 100 times smaller.Comment: 9 pages, 9 figures, Revtex, to appear in Phys. Rev.
Explicitly Covariant Light-Front Dynamics and Relativistic Few-Body Systems
The wave function of a composite system is defined in relativity on a
space-time surface. In the explicitly covariant light-front dynamics, reviewed
in the present article, the wave functions are defined on the plane \omega \cd
x=0, where is an arbitrary four-vector with . The
standard non-covariant approach is recovered as a particular case for . Using the light-front plane is of crucial importance, while the
explicit covariance gives strong advantages emphasized through all the review.
The properties of the relativistic few-body wave functions are discussed in
detail and are illustrated by examples in a solvable model. The
three-dimensional graph technique for the calculation of amplitudes in the
covariant light-front perturbation theory is presented.
The structure of the electromagnetic amplitudes is studied. We investigate
the ambiguities which arise in any approximate light-front calculations, and
which lead to a non-physical dependence of the electromagnetic amplitude on the
orientation of the light-front plane. The elastic and transition form factors
free from these ambiguities are found for spin 0, 1/2 and 1 systems.
The formalism is applied to the calculation of the relativistic wave
functions of two-nucleon systems (deuteron, scattering state), with particular
attention to the role of their new components in the deuteron elastic and
electrodisintegration form factors and to their connection with meson exchange
currents. Straigthforward applications to the pion and nucleon form factors and
the transition are also made.Comment: latex.tar.gz file, 162 pages, 42 figures, to be published in Physics
Reports (next issues
PEBSI - A Monte Carlo simulator for bremsstrahlung arising from electrons colliding with thin solid-state targets
We present a Monte Carlo code dedicated to the simulation of bremsstrahlung
arising in collisions of polarized electrons with thin target foils. The
program consists of an electron transport algorithm taking into account elastic
electron-nucleus scattering and inelastic collisions with target electrons as
well as a treatment of polarized-electron bremsstrahlung emission. Good
agreement is found between the predictions of the electron transport code and
data stemming from other simulation programs and experiments. In addition, we
present first results from the bremsstrahlung simulation which indicate a
significant decrease in the degree of linear polarization of bremsstrahlung
even for the thinnest gold targets considered
Pion-photon and photon-pion transition form factors in light-cone formalism
We derive the minimal Fock-state expansions of the pion and the photon wave
functions in light-cone formalism, then we calculate the pion-photon and the
photon-pion transition form factors of and
processes by employing these
quark-antiquark wave functions of the pion and the photon. We find that our
calculation for the transition form factor
agrees with the experimental data at low and moderately high energy scale.
Moreover, the physical differences and inherent connections between the
transition form factors of and have been illustrated, which indicate that these
two physical processes are intrinsically related. In addition, we also discuss
the form factor and the decay width at .Comment: 20 pages, 2 figure
Superhard Phases of Simple Substances and Binary Compounds of the B-C-N-O System: from Diamond to the Latest Results (a Review)
The basic known and hypothetic one- and two-element phases of the B-C-N-O
system (both superhard phases having diamond and boron structures and
precursors to synthesize them) are described. The attention has been given to
the structure, basic mechanical properties, and methods to identify and
characterize the materials. For some phases that have been recently described
in the literature the synthesis conditions at high pressures and temperatures
are indicated.Comment: Review on superhard B-C-N-O phase
Current Fluctuations and Electron-Electron Interactions in Coherent Conductors
We analyze current fluctuations in mesoscopic coherent conductors in the
presence of electron-electron interactions. In a wide range of parameters we
obtain explicit universal dependencies of the current noise on temperature,
voltage and frequency. We demonstrate that Coulomb interaction decreases the
Nyquist noise. In this case the interaction correction to the noise spectrum is
governed by the combination , where is the transmission
of the -th conducting mode. The effect of electron-electron interactions on
the shot noise is more complicated. At sufficiently large voltages we recover
two different interaction corrections entering with opposite signs. The net
result is proportional to , i.e. Coulomb interaction
decreases the shot noise at low transmissions and increases it at high
transmissions.Comment: 16 pages, 2 figure
Geometry and material effects in Casimir physics - Scattering theory
We give a comprehensive presentation of methods for calculating the Casimir
force to arbitrary accuracy, for any number of objects, arbitrary shapes,
susceptibility functions, and separations. The technique is applicable to
objects immersed in media other than vacuum, to nonzero temperatures, and to
spatial arrangements in which one object is enclosed in another. Our method
combines each object's classical electromagnetic scattering amplitude with
universal translation matrices, which convert between the bases used to
calculate scattering for each object, but are otherwise independent of the
details of the individual objects. This approach, which combines methods of
statistical physics and scattering theory, is well suited to analyze many
diverse phenomena. We illustrate its power and versatility by a number of
examples, which show how the interplay of geometry and material properties
helps to understand and control Casimir forces. We also examine whether
electrodynamic Casimir forces can lead to stable levitation. Neglecting
permeabilities, we prove that any equilibrium position of objects subject to
such forces is unstable if the permittivities of all objects are higher or
lower than that of the enveloping medium; the former being the generic case for
ordinary materials in vacuum.Comment: 44 pages, 11 figures, to appear in upcoming Lecture Notes in Physics
volume in Casimir physic
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