2,255 research outputs found
On the approach to equilibrium of an Hamiltonian chain of anharmonic oscillators
In this note we study the approach to equilibrium of a chain of anharmonic
oscillators. We find indications that a sufficiently large system always
relaxes to the usual equilibrium distribution. There is no sign of an
ergodicity threshold. The time however to arrive to equilibrium diverges when
, being the anharmonicity.Comment: 8 pages, 5 figure
A pseudo-potential analog for zero-range photoassociation and Feshbach resonance
A zero-range approach to atom-molecule coupling is developed in analogy to
the Fermi-Huang pseudo-potential treatment of atom-atom interactions. It is
shown by explicit comparison to an exactly-solvable finite-range model that
replacing the molecular bound-state wavefunction with a regularized
delta-function can reproduce the exact scattering amplitude in the
long-wavelength limit. Using this approach we find an analytical solution to
the two-channel Feshbach resonance problem for two atoms in a spherical
harmonic trap
The Consistency of Fermi-LAT Observations of the Galactic Center with a Millisecond Pulsar Population in the Central Stellar Cluster
I show that the spectrum and morphology of a recent Fermi-LAT observation of
the Galaxy center are consistent with a millisecond pulsar population in the
nuclear Central stellar cluster of the Milky Way. The Galaxy Center gamma-ray
spectrum is consistent with the spectrum of four of eight globular clusters
that have been detected in the gamma-ray. A dark matter annihilation
interpretation cannot be ruled out, though no unique features exist that would
require this conclusion.Comment: 5 pages, 1 figure; v3: matches version to appear in JCA
Atomic Effective Pseudopotentials for Semiconductors
We derive an analytic connection between the screened self-consistent
effective potential from density functional theory (DFT) and atomic effective
pseudopotentials (AEPs). The motivation to derive AEPs is to address structures
with thousands to hundred thousand atoms, as given in most nanostructures. The
use of AEPs allows to bypass a self-consistent procedure and to address
eigenstates around a certain region of the spectrum (e.g., around the band
gap). The bulk AEP construction requires two simple DFT calculations of
slightly deformed elongated cells. The ensuing AEPs are given on a fine
reciprocal space grid, including the small reciprocal vector components, are
free of parameters, and involve no fitting procedure. We further show how to
connect the AEPs of different bulk materials, which is necessary to obtain
accurate band offsets. We derive a total of 20 AEPs for III-V, II-VI and group
IV semiconductors and demonstrate their accuracy and transferability by
comparison to DFT calculations of strained bulk structures, quantum wells with
varying thickness, and semiconductor alloys.Comment: 10 pages, 5 figures, submitted to PR
Classical evolution of fractal measures generated by a scalar field on the lattice
We investigate the classical evolution of a scalar field theory,
using in the initial state random field configurations possessing a fractal
measure expressed by a non-integer mass dimension. These configurations
resemble the equilibrium state of a critical scalar condensate. The measures of
the initial fractal behavior vary in time following the mean field motion. We
show that the remnants of the original fractal geometry survive and leave an
imprint in the system time averaged observables, even for large times compared
to the approximate oscillation period of the mean field, determined by the
model parameters. This behavior becomes more transparent in the evolution of a
deterministic Cantor-like scalar field configuration. We extend our study to
the case of two interacting scalar fields, and we find qualitatively similar
results. Therefore, our analysis indicates that the geometrical properties of a
critical system initially at equilibrium could sustain for several periods of
the field oscillations in the phase of non-equilibrium evolution.Comment: 13 pages, 13 figures, version published at Int. J. Mod. Phys.
Causality, delocalization and positivity of energy
In a series of interesting papers G. C. Hegerfeldt has shown that quantum
systems with positive energy initially localized in a finite region,
immediately develop infinite tails. In our paper Hegerfeldt's theorem is
analysed using quantum and classical wave packets. We show that Hegerfeldt's
conclusion remains valid in classical physics. No violation of Einstein's
causality is ever involved. Using only positive frequencies, complex wave
packets are constructed which at are real and finitely localized and
which, furthemore, are superpositions of two nonlocal wave packets. The
nonlocality is initially cancelled by destructive interference. However this
cancellation becomes incomplete at arbitrary times immediately afterwards. In
agreement with relativity the two nonlocal wave packets move with the velocity
of light, in opposite directions.Comment: 14 pages, 5 figure
The e+ e- -> P1 P2 gamma processes close to the Phi peak: toward a model-independent analysis
We discuss the general decomposition and possible general parameterizations
of the processes , where , , or , for .
Particular attention is devoted to the amplitude where the two pseudoscalar
mesons are in a state, where we propose a general
parameterization which should help to shed light on the nature of light scalar
mesons.Comment: 12 pages, Late
Ionization potentials in the limit of large atomic number
By extrapolating the energies of non-relativistic atoms and their ions with
up to 3000 electrons within Kohn-Sham density functional theory, we find that
the ionization potential remains finite and increases across a row, even as
. The local density approximation becomes chemically
accurate (and possibly exact) in some cases. Extended Thomas-Fermi theory
matches the shell-average of both the ionization potential and density change.
Exact results are given in the limit of weak electron-electron repulsion.Comment: 4 pages, 5 figure
Dark Matter detection via lepton cosmic rays
Recent observations of lepton cosmic rays, coming from the PAMELA and FERMI
experiments, have pushed our understanding of the interstellar medium and
cosmic rays sources to unprecedented levels. The imprint of dark matter on
lepton cosmic rays is the most exciting explanation of both PAMELA's positron
excess and FERMI's total flux of electrons. Alternatively, supernovae are
astrophysical objects with the same potential to explain these observations. In
this work, we present an updated study of the astrophysical sources of lepton
cosmic rays and the possible trace of a dark matter signal on the positron
excess and total flux of electrons.Comment: 6 pages and 3 figures. Proceedings for PASCOS 2010, Valencia, Spai
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