1,111 research outputs found
Local virial relation and velocity anisotropy for collisionless self-gravitating systems
The collisionless quasi-equilibrium state realized after the cold collapse of
self-gravitating systems has two remarkable characters. One of them is the
linear temperature-mass (TM) relation, which yields a characteristic
non-Gaussian velocity distribution. Another is the local virial (LV) relation,
the virial relation which holds even locally in collisionless systems through
phase mixing such as cold-collapse. A family of polytropes are examined from a
view point of these two characters. The LV relation imposes a strong constraint
on these models: only polytropes with index with a flat boundary
condition at the center are compatible with the numerical results, except for
the outer region. Using the analytic solutions based on the static and
spherical Jeans equation, we show that this incompatibility in the outer region
implies the important effect of anisotropy of velocity dispersion. Furthermore,
the velocity anisotropy is essential in explaining various numerical results
under the condition of the local virial relation.Comment: 8 pages, 5 figures, Proceedings of CN-Kyoto International Workshop on
Complexity and Nonextensivity; added a reference for section
Electronic structure of the strongly hybridized ferromagnet CeFe2
We report on results from high-energy spectroscopic measurements on CeFe2, a
system of particular interest due to its anomalous ferromagnetism with an
unusually low Curie temperature and small magnetization compared to the other
rare earth-iron Laves phase compounds. Our experimental results indicate very
strong hybridization of the Ce 4f states with the delocalized band states,
mainly the Fe 3d states. In the interpretation and analysis of our measured
spectra, we have made use of two different theoretical approaches: The first
one is based on the Anderson impurity model, with surface contributions
explicitly taken into account. The second method consists of band-structure
calculations for bulk CeFe2. The analysis based on the Anderson impurity model
gives calculated spectra in good agreement with the whole range of measured
spectra, and reveals that the Ce 4f -- Fe 3d hybridization is considerably
reduced at the surface, resulting in even stronger hybridization in the bulk
than previously thought. The band-structure calculations are ab initio
full-potential linear muffin-tin orbital calculations within the
local-spin-density approximation of the density functional. The Ce 4f electrons
were treated as itinerant band electrons. Interestingly, the Ce 4f partial
density of states obtained from the band-structure calculations also agree well
with the experimental spectra concerning both the 4f peak position and the 4f
bandwidth, if the surface effects are properly taken into account. In addition,
results, notably the partial spin magnetic moments, from the band-structure
calculations are discussed in some detail and compared to experimental findings
and earlier calculations.Comment: 10 pages, 8 figures, to appear in Phys. Rev. B in December 200
Microphysical Approach to Nonequilibrium Dynamics of Quantum Fields
We examine the nonequilibrium dynamics of a self-interacting
scalar field theory. Using a real time formulation of finite temperature field
theory we derive, up to two loops and , the effective equation of
motion describing the approach to equilibrium. We present a detailed analysis
of the approximations used in order to obtain a Langevin-like equation of
motion, in which the noise and dissipation terms associated with quantum
fluctuations obey a fluctuation-dissipation relation. We show that, in general,
the noise is colored (time-dependent) and multiplicative (couples nonlinearly
to the field), even though it is still Gaussian distributed. The noise becomes
white in the infinite temperature limit. We also address the effect of
couplings to other fields, which we assume play the r\^ole of the thermal bath,
in the effective equation of motion for . In particular, we obtain the
fluctuation and noise terms due to a quadratic coupling to another scalar
field.Comment: 30 pages, LaTex (uses RevTex 3.0), DART-HEP-93/0
Absence of isentropic expansion in various inflation models
Dynamics of the inflaton is studied when it interacts with boson and fermion
fields and in minimal supersymmetric models. This encompasses multifield
inflation models, such as hybrid inflation, and typical reheating models. For
much of the parameter space conducive to inflation, the inflaton is found to
dissipate adequate radiation to have observational effects on density
perturbations and in cases to significantly affect inflaton evolution. Thus,
for many inflation models, believed to yield exclusively isentropic inflation,
the parameter space now divides into regimes of isentropic and nonisentropic
inflation.Comment: 6 pages, 1 figure. Version in press Phys. Lett.
Classical Fields Near Thermal Equilibrium
We discuss the classical limit for the long-distance (``soft'') modes of a
quantum field when the hard modes of the field are in thermal equilibrium. We
address the question of the correct semiclassical dynamics when a momentum
cut-off is introduced. Higher order contributions leads to a stochastic
interpretation for the effective action in analogy to Quantum Brownian Motion,
resulting in dissipation and decoherence for the evolution of the soft modes.
Particular emphasis is put on the understanding of dissipation. Our discussion
focuses mostly on scalar fields, but we make some remarks on the extension to
gauge theories.Comment: REVTeX, 6 figure
Fermi Surface of 3d^1 Perovskite CaVO3 Near the Mott Transition
We present a detailed de Haas van Alphen effect study of the perovskite
CaVO3, offering an unprecedented test of electronic structure calculations in a
3d transition metal oxide. Our experimental and calculated Fermi surfaces are
in good agreement -- but only if we ignore large orthorhombic distortions of
the cubic perovskite structure. Subtle discrepancies may shed light on an
apparent conflict between the low energy properties of CaVO3, which are those
of a simple metal, and high energy probes which reveal strong correlations that
place CaVO3 on the verge of a metal-insulator transition.Comment: 4 pages, 4 figures (REVTeX
Dynamical System Analysis for Inflation with Dissipation
We examine the solutions of the equations of motion for an expanding
Universe, taking into account the radiation of the inflaton field energy. We
then analyze the question of the generality of inflationary solutions in this
more general setting of a dissipative system. We find a surprisingly rich
behavior for the solutions of the dynamical system of equations in the presence
of dissipational effects. We also determine that a value of dissipation as
small as can lead to a smooth exit from inflation to
radiation.Comment: Plain LaTex, 21 pages, 8 eps figs (uses epsf), to be published in
Phys. Rev.
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