5,110 research outputs found
The âStandardâ Administrative Procedure for Supervising and Enforcing EC Law: EC Treaty Articles 226 and 228
Ibanez examines the European Commission\u27s policy and strategy in enforcement proceedings and attempts to discover the predominant European model, if such a model exists, for enforcing and supervising EC law. Ibanez focuses on some general difficulties in analyzing supervision and enforcement at the European level and the problem of implementation in more general terms
Quintessence and Supergravity
In the context of quintessence, the concept of tracking solutions allows to
address the fine-tuning and coincidence problems. When the field is on tracks
today, one has demonstrating that, generically, any
realistic model of quintessence must be based on supergravity. We construct the
most simple model for which the scalar potential is positive. The scalar
potential deduced from the supergravity model has the form
. We show
that despite the appearence of positive powers of the field, the coincidence
problem is still solved. If , the fine-tuning problem can be
overcome. Moreover, due to the presence of the exponential term, the value of
the equation of state, , is pushed towards the value -1 in contrast
to the usual case for which it is difficult to go beyond . For , the model presented here predicts
. Finally, we establish the
relation for this model.Comment: 9 pages, 4 figures. Accepted for publication in Physics Letters B.
Numerical value of \omega_Q changed: correct value is -0.82. New references
and one figure adde
Legendre expansion of the neutrino-antineutrino annihilation kernel: Influence of high order terms
We calculate the Legendre expansion of the rate of the process up to 3rd order extending previous results
of other authors which only consider the 0th and 1st order terms. Using
different closure relations for the moment equations of the radiative transfer
equation we discuss the physical implications of taking into account quadratic
and cubic terms on the energy deposition outside the neutrinosphere in a
simplified model. The main conclusion is that 2nd order is necessary in the
semi-transparent region and gives good results if an appropriate closure
relation is used.Comment: 14 pages, 4 figures. To be published in A&A Supplement Serie
Galaxy clusters and microwave background anisotropy
Previous estimates of the microwave background anisotropies produced by
freely falling spherical clusters are discussed. These estimates are based on
the Swiss-Cheese and Tolman-Bondi models. It is proved that these models give
only upper limits to the anisotropies produced by the observed galaxy clusters.
By using spherically symmetric codes including pressureless matter and a hot
baryonic gas, new upper limits are obtained. The contributions of the hot gas
and the pressureless component to the total anisotropy are compared. The
effects produced by the pressure are proved to be negligible; hence,
estimations of the cluster anisotropies based on N-body simulations are
hereafter justified. After the phenomenon of violent relaxation, any realistic
rich cluster can only produce small anisotropies with amplitudes of order
. During the rapid process of violent relaxation, the anisotropies
produced by nonlinear clusters are expected to range in the interval
. The angular scales of these anisotropies are discussed.Comment: 31 pages, 3 postscript figures, accepted MNRA
Adjoint Chiral Supermultiplets and Their Phenomenology
Matter fields in the MSSM are chiral supermultiplets in fundamental (or
singlet) representations of the standard model gauge group. In this paper we
introduce chiral superfields in the adjoint representation of and
study the effective field theory and phenomenology of them. These states are
well motivated by intersecting D-brane models in which additional massless
adjoint chiral supermultiplets appear generically in the low energy spectrum.
Although it has been pointed out that the existence of these additional fields
may make it difficult to obtain asymptotic freedom, we demonstrate that this
consideration does not rule out the existence of adjoints. The QCD gauge
coupling can be perturbative up to a sufficiently high scale, and therefore a
perturbative description for a D-brane model is valid. The full supersymmetric
and soft SUSY breaking Lagrangians and the resulting renormalization group
equations are given. Phenomenological aspects of the adjoint matter are also
studied, including the decay and production processes. The similarity in gauge
interaction between the adjoint fermion and gluino facilitates our study on
these aspects. It is found that these adjoint multiplets can give detectable
signals at colliders and satisfy the constraints from cosmology.Comment: 18 pages, 3 figures; minor corrections, references adde
Numerical evolution of matter in dynamical axisymmetric black hole spacetimes. I. Methods and tests
We have developed a numerical code to study the evolution of self-gravitating
matter in dynamic black hole axisymmetric spacetimes in general relativity. The
matter fields are evolved with a high-resolution shock-capturing scheme that
uses the characteristic information of the general relativistic hydrodynamic
equations to build up a linearized Riemann solver. The spacetime is evolved
with an axisymmetric ADM code designed to evolve a wormhole in full general
relativity. We discuss the numerical and algorithmic issues related to the
effective coupling of the hydrodynamical and spacetime pieces of the code, as
well as the numerical methods and gauge conditions we use to evolve such
spacetimes. The code has been put through a series of tests that verify that it
functions correctly. Particularly, we develop and describe a new set of testbed
calculations and techniques designed to handle dynamically sliced,
self-gravitating matter flows on black holes, and subject the code to these
tests. We make some studies of the spherical and axisymmetric accretion onto a
dynamic black hole, the fully dynamical evolution of imploding shells of dust
with a black hole, the evolution of matter in rotating spacetimes, the
gravitational radiation induced by the presence of the matter fields and the
behavior of apparent horizons through the evolution.Comment: 42 pages, 20 figures, submitted to Phys Rev
Hyperbolic character of the angular moment equations of radiative transfer and numerical methods
We study the mathematical character of the angular moment equations of
radiative transfer in spherical symmetry and conclude that the system is
hyperbolic for general forms of the closure relation found in the literature.
Hyperbolicity and causality preservation lead to mathematical conditions
allowing to establish a useful characterization of the closure relations. We
apply numerical methods specifically designed to solve hyperbolic systems of
conservation laws (the so-called Godunov-type methods), to calculate numerical
solutions of the radiation transport equations in a static background. The
feasibility of the method in any kind of regime, from diffusion to
free-streaming, is demonstrated by a number of numerical tests and the effect
of the choice of the closure relation on the results is discussed.Comment: 37 pags, 12 figures, accepted for publication in MNRA
Leibniz algebroid associated with a Nambu-Poisson structure
The notion of Leibniz algebroid is introduced, and it is shown that each
Nambu-Poisson manifold has associated a canonical Leibniz algebroid. This fact
permits to define the modular class of a Nambu-Poisson manifold as an
appropiate cohomology class, extending the well-known modular class of Poisson
manifolds
- âŠ