12,832 research outputs found
Localization and chiral symmetry in 2+1 flavor domain wall QCD
We present results for the dependence of the residual mass of domain wall
fermions (DWF) on the size of the fifth dimension and its relation to the
density and localization properties of low-lying eigenvectors of the
corresponding hermitian Wilson Dirac operator relevant to simulations of 2+1
flavor domain wall QCD. Using the DBW2 and Iwasaki gauge actions, we generate
ensembles of configurations with a space-time volume and an
extent of 8 in the fifth dimension for the sea quarks. We demonstrate the
existence of a regime where the degree of locality, the size of chiral symmetry
breaking and the rate of topology change can be acceptable for inverse lattice
spacings GeV.Comment: 59 Pages, 23 figures, 1 MPG linke
Two-dimensional approach to relativistic positioning systems
A relativistic positioning system is a physical realization of a coordinate
system consisting in four clocks in arbitrary motion broadcasting their proper
times. The basic elements of the relativistic positioning systems are presented
in the two-dimensional case. This simplified approach allows to explain and to
analyze the properties and interest of these new systems. The positioning
system defined by geodesic emitters in flat metric is developed in detail. The
information that the data generated by a relativistic positioning system give
on the space-time metric interval is analyzed, and the interest of these
results in gravimetry is pointed out.Comment: 11 pages, 5 figures. v2: a brief description of the principal
bibliography has been adde
How does the geodesic rule really work for global symmetry breaking first order phase transitions?
The chain of events usually understood to lead to the formation of
topological defects during phase transitions is known as the Kibble mechanism.
A central component of the mechanism is the so-called ``geodesic rule''.
Although in the Abelian Higgs model the validity of the geodesic rule has been
questioned recently, it is known to be valid on energetic grounds for a global
U(1) symmetry breaking transition. However, even for these globally symmetric
models no dynamical analisys of the rule has been carried to this date, and
some points as to how events proceed still remain obscure. This paper tries to
clarify the dynamics of the geodesic rule in the context of a global U(1)
model. With an appropriate ansatz for the field modulus we find a family of
analytical expressions, phase walls, that accounts for both geodesic and
nongeodesic configurations. We then show how the latter ones are unstable and
decay into the former by nucleating pairs of defects. Finnally, we try to give
a physical perspective of how the geodesic rule might really work in these
transitions.Comment: 10 pages, 9 multiple figre
Hierarchical Model for the Evolution of Cloud Complexes
The structure of cloud complexes appears to be well described by a "tree
structure" representation when the image is partitioned into "clouds". In this
representation, the parent-child relationships are assigned according to
containment. Based on this picture, a hierarchical model for the evolution of
Cloud Complexes, including star formation, is constructed, that follows the
mass evolution of each sub-structure by computing its mass exchange
(evaporation or condensation) with its parent and children, which depends on
the radiation density at the interphase. For the set of parameters used as a
reference model, the system produces IMFs with a maximum at too high mass (~2
M_sun) and the characteristic times for evolution seem too long. We show that
these properties can be improved by adjusting model parameters. However, the
emphasis here is to illustrate some general properties of this nonlinear model
for the star formation process. Notwithstanding the simplifications involved,
the model reveals an essential feature that will likely remain if additional
physical processes are included. That is: the detailed behavior of the system
is very sensitive to variations on the initial and external conditions,
suggesting that a "universal" IMF is very unlikely. When an ensemble of IMFs
corresponding to a variety of initial or external conditions is examined, the
slope of the IMF at high masses shows variations comparable to the range
derived from observational data. (Abridged)Comment: Latex, 29 pages, 13 figures, accepted for publication in Ap
Defect free global minima in Thomson's problem of charges on a sphere
Given unit points charges on the surface of a unit conducting sphere,
what configuration of charges minimizes the Coulombic energy ? Due to an exponential rise in good local minima, finding global
minima for this problem, or even approaches to do so has proven extremely
difficult. For \hbox{} recent theoretical work based on
elasticity theory, and subsequent numerical work has shown, that for --1000 adding dislocation defects to a symmetric icosadeltahedral lattice
lowers the energy. Here we show that in fact this approach holds for all ,
and we give a complete or near complete catalogue of defect free global minima.Comment: Revisions in Tables and Reference
Addition theorems for spin spherical harmonics. II Results
Based on the results of part I, we obtain the general form of the addition
theorem for spin spherical harmonics and give explicit results in the cases
involving one spin- and one spin- spherical harmonics with ,
1, 3/2, and , 1. We obtain also a fully general addition theorem for
one scalar and one tensor spherical harmonic of arbitrary rank. A variety of
bilocal sums of ordinary and spin spherical harmonics are given in explicit
form, including a general explicit expression for bilocal spherical harmonics
Full Causal Bulk Viscous Cosmologies with time-varying Constants
We study the evolution of a flat Friedmann-Robertson-Walker Universe, filled
with a bulk viscous cosmological fluid, in the presence of time varying
``constants''. The dimensional analysis of the model suggests a proportionality
between the bulk viscous pressure of the dissipative fluid and the energy
density. On using this assumption and with the choice of the standard equations
of state for the bulk viscosity coefficient, temperature and relaxation time,
the general solution of the field equations can be obtained, with all physical
parameters having a power-law time dependence. The symmetry analysis of this
model, performed by using Lie group techniques, confirms the unicity of the
solution for this functional form of the bulk viscous pressure. In order to
find another possible solution we relax the hypotheses assuming a concrete
functional dependence for the ``constants''.Comment: 28 pages, RevTeX
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