22,112 research outputs found
Virtual Compton Scattering from the Proton and the Properties of Nucleon Excited States
We calculate the contributions to the generalized polarizabilities of
the proton in virtual Compton scattering. The following nucleon excitations are
included: , , , , ,
and . The relationship between nucleon
structure parameters, properties and the generalized polarizabilities of
the proton is illustrated.Comment: 13 pages of text (Latex) plus 4 figures (as uuencoded Z-compressed
.tar file created by csh script uufiles
Groups of graphs of groups
We classify all groups of color preserving automorphisms (isometries) of edge colored complete graphs derived from finite groups
Analytical solution of the dynamical spherical MIT bag
We prove that when the bag surface is allowed to move radially, the equations
of motion derived from the MIT bag Lagrangian with massless quarks and a
spherical boundary admit only one solution, which corresponds to a bag
expanding at the speed of light. This result implies that some new physics
ingredients, such as coupling to meson fields, are needed to make the dynamical
bag a consistent model of hadrons.Comment: Revtex, no figures. Submitted to Journal of Physics
Extracting Scattering Phase-Shifts in Higher Partial-Waves from Lattice QCD Calculations
L\"uscher's method is routinely used to determine meson-meson, meson-baryon
and baryon-baryon s-wave scattering amplitudes below inelastic thresholds from
Lattice QCD calculations - presently at unphysical light-quark masses. In this
work we review the formalism and develop the requisite expressions to extract
phase-shifts describing meson-meson scattering in partial-waves with
angular-momentum l<=6 and l=9. The implications of the underlying cubic
symmetry, and strategies for extracting the phase-shifts from Lattice QCD
calculations, are presented, along with a discussion of the signal-to-noise
problem that afflicts the higher partial-waves.Comment: 79 pages, 41 figure
Weak local rules for planar octagonal tilings
We provide an effective characterization of the planar octagonal tilings
which admit weak local rules. As a corollary, we show that they are all based
on quadratic irrationalities, as conjectured by Thang Le in the 90s.Comment: 23 pages, 6 figure
High pressure evolution of FeO electronic structure revealed by X-ray absorption
We report the first high pressure measurement of the Fe K-edge in hematite
(FeO) by X-ray absorption spectroscopy in partial fluorescence yield
geometry. The pressure-induced evolution of the electronic structure as
FeO transforms from a high-spin insulator to a low-spin metal is
reflected in the x-ray absorption pre-edge. The crystal field splitting energy
was found to increase monotonically with pressure up to 48 GPa, above which a
series of phase transitions occur. Atomic multiplet, cluster diagonalization,
and density-functional calculations were performed to simulate the pre-edge
absorption spectra, showing good qualitative agreement with the measurements.
The mechanism for the pressure-induced phase transitions of FeO is
discussed and it is shown that ligand hybridization significantly reduces the
critical high-spin/low-spin pressure.Comment: 5 pages, 4 figures and 1 tabl
Entanglement entropy in collective models
We discuss the behavior of the entanglement entropy of the ground state in
various collective systems. Results for general quadratic two-mode boson models
are given, yielding the relation between quantum phase transitions of the
system (signaled by a divergence of the entanglement entropy) and the
excitation energies. Such systems naturally arise when expanding collective
spin Hamiltonians at leading order via the Holstein-Primakoff mapping. In a
second step, we analyze several such models (the Dicke model, the two-level BCS
model, the Lieb-Mattis model and the Lipkin-Meshkov-Glick model) and
investigate the properties of the entanglement entropy in the whole parameter
range. We show that when the system contains gapless excitations the
entanglement entropy of the ground state diverges with increasing system size.
We derive and classify the scaling behaviors that can be met.Comment: 11 pages, 7 figure
Time Dependent Monte Carlo Radiative Transfer Calculations For 3-Dimensional Supernova Spectra, Lightcurves, and Polarization
We discuss Monte-Carlo techniques for addressing the 3-dimensional
time-dependent radiative transfer problem in rapidly expanding supernova
atmospheres. The transfer code SEDONA has been developed to calculate the
lightcurves, spectra, and polarization of aspherical supernova models. From the
onset of free-expansion in the supernova ejecta, SEDONA solves the radiative
transfer problem self-consistently, including a detailed treatment of gamma-ray
transfer from radioactive decay and with a radiative equilibrium solution of
the temperature structure. Line fluorescence processes can also be treated
directly. No free parameters need be adjusted in the radiative transfer
calculation, providing a direct link between multi-dimensional hydrodynamical
explosion models and observations. We describe the computational techniques
applied in SEDONA, and verify the code by comparison to existing calculations.
We find that convergence of the Monte Carlo method is rapid and stable even for
complicated multi-dimensional configurations. We also investigate the accuracy
of a few commonly applied approximations in supernova transfer, namely the
stationarity approximation and the two-level atom expansion opacity formalism.Comment: 16 pages, ApJ accepte
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