25,978 research outputs found
Anomaly candidates and invariants of D=4, N=1 supergravity theories
All anomaly candidates and the form of the most general invariant local
action are given for old and new minimal supergravity, including the cases
where additional Yang--Mills and chiral matter multiplets are present.
Furthermore nonminimal supergravity is discussed. In this case local
supersymmetry itself may be anomalous and some of the corresponding anomaly
candidates are given explicitly. The results are obtained by solving the
descent equations which contain the consistency equation satisfied by
integrands of anomalies and invariant actions.Comment: 19 pages, LaTex, NIKHEF-H 93-12, ITP-UH 07/9
Some New Exact Ground States for Generalize Hubbard Models
A set of new exact ground states of the generalized Hubbard models in
arbitrary dimensions with explicitly given parameter regions is presented. This
is based on a simple method for constructing exact ground states for
homogeneous quantum systems.Comment: 9 pages, Late
An Axisymmetric Gravitational Collapse Code
We present a new numerical code designed to solve the Einstein field
equations for axisymmetric spacetimes. The long term goal of this project is to
construct a code that will be capable of studying many problems of interest in
axisymmetry, including gravitational collapse, critical phenomena,
investigations of cosmic censorship, and head-on black hole collisions. Our
objective here is to detail the (2+1)+1 formalism we use to arrive at the
corresponding system of equations and the numerical methods we use to solve
them. We are able to obtain stable evolution, despite the singular nature of
the coordinate system on the axis, by enforcing appropriate regularity
conditions on all variables and by adding numerical dissipation to hyperbolic
equations.Comment: 19 pages, 9 figure
El Roque de Los Muchachos Site Characteristics. II. Analysis of Wind, Relative Humidity and Air Pressure
In this paper we present an analysis of wind speed, wind direction, relative
humidity and air pressure taken at TNG, CAMC and NOT at Observatorio del Roque
de Los Muchachos, in the Canary Islands. Data are compared in order to check
local variations and both long term and short term trends of the microclimate.
Furthermore, influence of wind speed on the astronomical seeing is estimated to
the aim to better understand the influence of wide scale parameters on local
meteorological data. The three telescopes show different prevailing wind
direction, wind speed, relative humidity and air pressure confirming
differences in local microclimate. We found that seeing deteriorates when wind
speed is lower than 3.3 m/s. Comparison in terms of wind speed and high
relative humidity (> 90%) shows that TNG seems to have optimal observational
conditions with respect to CAMC and NOT. Air pressure analysis shows that ORM
is dominated by high pressure. Short time variations of pressure anticipate
temperature variations tipically by 2-3 hours, this property vanishes in time
scales higher than some hours and disappear in longer time scales.Comment: 10 pages, 9 figures, accepted for publication in PAS
Charge-ordered ferromagnetic phase in manganites
A mechanism for charge-ordered ferromagnetic phase in manganites is proposed.
The mechanism is based on the double exchange in the presence of diagonal
disorder. It is modeled by a combination of the Ising double-exchange and the
Falicov-Kimball model. Within the dynamical mean-field theory the charge and
spin correlation function are explicitely calculated. It is shown that the
system exhibits two successive phase transitions. The first one is the
ferromagnetic phase transition, and the second one is a charge ordering. As a
result a charge-ordered ferromagnetic phase is stabilized at low temperature.Comment: To appear in Phys. Rev.
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
Variational theory of flux-line liquids
We formulate a variational (Hartree like) description of flux line liquids
which improves on the theory we developed in an earlier paper [A.M. Ettouhami,
Phys. Rev. B 65, 134504 (2002)]. We derive, in particular, how the massive term
confining the fluctuations of flux lines varies with temperature and show that
this term vanishes at high enough temperatures where the vortices behave as
freely fluctuating elastic lines.Comment: 10 pages, 1 postscript figur
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