11,659 research outputs found
Monitoring the localization-delocalization transition within a 1D model with non-random long-range interaction
We consider a two-parameter one-dimensional Hamiltonian with uncorrelated
diagonal disorder and {\it non-random} long-range inter-site interaction
. The model is critical at and reveals the
localization-delocalization transition with respect to the disorder magnitude.
To detect the transition we analyze level and wave function statistics. It is
demonstrated also that in the marginal case () all states are
localized.Comment: 4 pages, 5 figure
Comment on current correlators in QCD at finite temperature
We address some criticisms by Eletsky and Ioffe on the extension of QCD sum
rules to finite temperature. We argue that this extension is possible, provided
the Operator Product Expansion and QCD-hadron duality remain valid at non-zero
temperature. We discuss evidence in support of this from QCD, and from the
exactly solvable two- dimensional sigma model O(N) in the large N limit, and
the Schwinger model.Comment: 10 pages, LATEX file, UCT-TP-208/94, April 199
Corrections to the Gell-Mann-Oakes-Renner relation and chiral couplings and
Next to leading order corrections to the
Gell-Mann-Oakes-Renner relation (GMOR) are obtained using weighted QCD Finite
Energy Sum Rules (FESR) involving the pseudoscalar current correlator. Two
types of integration kernels in the FESR are used to suppress the contribution
of the kaon radial excitations to the hadronic spectral function, one with
local and the other with global constraints. The result for the pseudoscalar
current correlator at zero momentum is , leading to the chiral corrections to GMOR: . The resulting uncertainties are mostly due to variations in the upper
limit of integration in the FESR, within the stability regions, and to a much
lesser extent due to the uncertainties in the strong coupling and the strange
quark mass. Higher order quark mass corrections, vacuum condensates, and the
hadronic resonance sector play a negligible role in this determination. These
results confirm an independent determination from chiral perturbation theory
giving also very large corrections, i.e. roughly an order of magnitude larger
than the corresponding corrections in chiral . Combining
these results with our previous determination of the corrections to GMOR in
chiral , , we are able to determine two low
energy constants of chiral perturbation theory, i.e. , and , both at the
scale of the -meson mass.Comment: Revised version with minor correction
Zero-energy peak of the density of states and localization properties of a one-dimensional Frenkel exciton: Off-diagonal disorder
We study a one-dimensional Frenkel Hamiltonian with off-diagonal disorder,
focusing our attention on the physical nature of the zero-energy peak of the
density of states. The character of excitonic states (localized or delocalized)
is also examined in the vicinity of this peak. It is shown that the state being
responsible for the peak is localized. A detailed comparison of the
nearest-neighbor approach with the long-range dipole-dipole coupling is
performed.Comment: 15 pages with 7 figures (REVTeX). To appear in Physical Review
Evolution of small-scale magnetic elements in the vicinity of granular-size swirl convective motions
Advances in solar instrumentation have led to a widespread usage of time
series to study the dynamics of solar features, specially at small spatial
scales and at very fast cadences. Physical processes at such scales are
determinant as building blocks for many others occurring from the lower to the
upper layers of the solar atmosphere and beyond, ultimately for understanding
the bigger picture of solar activity. Ground-based (SST) and space-borne
(Hinode) high-resolution solar data are analyzed in a quiet Sun region
displaying negative polarity small-scale magnetic concentrations and a cluster
of bright points observed in G-band and Ca II H images. The studied region is
characterized by the presence of two small-scale convective vortex-type plasma
motions, one of which appears to be affecting the dynamics of both, magnetic
features and bright points in its vicinity and therefore the main target of our
investigations. We followed the evolution of bright points, intensity
variations at different atmospheric heights and magnetic evolution for a set of
interesting selected regions. A description of the evolution of the
photospheric plasma motions in the region nearby the convective vortex is
shown, as well as some plausible cases for convective collapse detected in
Stokes profiles.Comment: 9 figure
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