1,698 research outputs found
Strange chiral nucleon form factors
We investigate the strange electric and magnetic form factors of the nucleon
in the framework of heavy baryon chiral perturbation theory to third order in
the chiral expansion. All counterterms can be fixed from data. In particular,
the two unknown singlet couplings can be deduced from the parity-violating
electron scattering experiments performed by the SAMPLE and the HAPPEX
collaborations. Within the given uncertainties, our analysis leads to a small
and positive electric strangeness radius, .
We also deduce the consequences for the upcoming MAMI A4 experiment.Comment: 7 pp, REVTeX, uses epsf, minor correction
K* nucleon hyperon form factors and nucleon strangeness
A crucial input for recent meson hyperon cloud model estimates of the nucleon
matrix element of the strangeness current are the nucleon-hyperon-K* (NYK*)
form factors which regularize some of the arising loops. Prompted by new and
forthcoming information on these form factors from hyperon-nucleon potential
models, we analyze the dependence of the loop model results for the
strange-quark observables on the NYK* form factors and couplings. We find, in
particular, that the now generally favored soft N-Lambda-K* form factors can
reduce the magnitude of the K* contributions in such models by more than an
order of magnitude, compared to previous results with hard form factors. We
also discuss some general implications of our results for hadronic loop models.Comment: 9 pages, 8 figures, new co-author, discussion extended to the
momentum dependence of the strange vector form factor
Hadronic Parity Violation and Inelastic Electron-Deuteron Scattering
We compute contributions to the parity-violating (PV) inelastic
electron-deuteron scattering asymmetry arising from hadronic PV. While hadronic
PV effects can be relatively important in PV threshold electro- disintegration,
we find that they are highly suppressed at quasielastic kinematics. The
interpretation of the PV quasielastic asymmetry is, thus, largely unaffected by
hadronic PV.Comment: 27 pages, 13 figures, uses REVTeX and BibTe
Parity violating target asymmetry in electron - proton scattering
We analyze the parity-violating (PV) components of the analyzing power in
elastic electron-proton scattering and discuss their sensitivity to the strange
quark contributions to the proton weak form factors. We point out that the
component of the analyzing power along the momentum transfer is independent of
the electric weak form factor and thus compares favorably with the PV beam
asymmetry for a determination of the strangeness magnetic moment. We also show
that the transverse component could be used for constraining the strangeness
radius. Finally, we argue that a measurement of both components could give
experimental information on the strangeness axial charge.Comment: 24 pages, Latex, 5 eps figures, submitted to Phys.Rev.
Absence of Persistent Magnetic Oscillations in Type-II Superconductors
We report on a numerical study intended to examine the possibility that
magnetic oscillations persist in type II superconductors beyond the point where
the pairing self-energy exceeds the normal state Landau level separation. Our
work is based on the self-consistent numerical solution for model
superconductors of the Bogoliubov-deGennes equations for the vortex lattice
state. In the regime where the pairing self-energy is smaller than the
cyclotron energy, magnetic oscillations resulting from Landau level
quantization are suppressed by the broadening of quasiparticle Landau levels
due to the non-uniform order parameter of the vortex lattice state, and by
splittings of the quasiparticle bands. Plausible arguments that the latter
effect can lead to a sign change of the fundamental harmonic of the magnetic
oscillations when the pairing self-energy is comparable to the cyclotron energy
are shown to be flawed. Our calculations indicate that magnetic oscillations
are strongly suppressed once the pairing self-energy exceeds the Landau level
separation.Comment: 7 pages, revtex, 7 postscript figure
Fictive Impurity Models: an Alternative Formulation of the Cluster Dynamical Mean Field Method
"Cluster" extensions of the dynamical mean field method to include longer
range correlations are discussed. It is argued that the clusters arising in
these methods are naturally interpreted not as actual subunits of a physical
lattice but as algorithms for computing coefficients in an orthogonal function
expansion of the momentum dependence of the electronic self-energy. The
difficulties with causality which have been found to plague cluster dynamical
mean field methods are shown to be related to the "ringing" phenomenon familiar
from Fourier analysis. The analogy is used to motivate proposals for simple
filtering methods to circumvent them. The formalism is tested by comparison to
low order perturbative calculations and self consistent solutions
Quantum impurity solvers using a slave rotor representation
We introduce a representation of electron operators as a product of a
spin-carry ing fermion and of a phase variable dual to the total charge (slave
quantum rotor). Based on this representation, a new method is proposed for
solving multi-orbital Anderson quantum impurity models at finite interaction
strength U. It consists in a set of coupled integral equations for the
auxiliary field Green's functions, which can be derived from a controlled
saddle-point in the limit of a large number of field components. In contrast to
some finite-U extensions of the non-crossing approximation, the new method
provides a smooth interpolation between the atomic limit and the weak-coupling
limit, and does not display violation of causality at low-frequency. We
demonstrate that this impurity solver can be applied in the context of
Dynamical Mean-Field Theory, at or close to half-filling. Good agreement with
established results on the Mott transition is found, and large values of the
orbital degeneracy can be investigated at low computational cost.Comment: 18 pages, 15 figure
The Strange Quark Contribution to the Proton's Magnetic Moment
We report a new determination of the strange quark contribution to the
proton's magnetic form factor at a four-momentum transfer Q2 = 0.1 (GeV/c)^2
from parity-violating e-p elastic scattering. The result uses a revised
analysis of data from the SAMPLE experiment which was carried out at the
MIT-Bates Laboratory. The data are combined with a calculation of the proton's
axial form factor GAe to determine the strange form factor GMs(Q2=0.1)=0.37 +-
0.20 +- 0.26 +- 0.07. The extrapolation of GMs to its Q2=0 limit and comparison
with calculations is also discussed.Comment: 6 pages, 1 figure, submitted to Phys. Lett.
Finite temperature scaling theory for the collapse of Bose-Einstein condensate
We show how to apply the scaling theory in an inhomogeneous system like
harmonically trapped Bose condensate at finite temperatures. We calculate the
temperature dependence of the critical number of particles by a scaling theory
within the Hartree-Fock approximation and find that there is a dramatic
increase in the critical number of particles as the condensation point is
approached.Comment: Published online [6 pages, 3 figures
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