22,451 research outputs found
Ediacaran Obduction of a Fore-Arc Ophiolite in SW Iberia: A Turning Point in the Evolving Geodynamic Setting of Peri- Gondwana
The Calzadilla Ophiolite is an ensemble of mafic and ultramafic rocks that represents the
transition between lower crust and upper mantle of a Cadomian (peri-Gondwanan) fore arc. Mapping and
structural analysis of the ophiolite demonstrates that it was obducted in latest Ediacaran times, because the
Ediacaran-Early Cambrian sedimentary series (Malcocinado Formation) discordantly covers it. The ophiolite
and emplacement-related structures are affected by Variscan deformation (Devonian-Carboniferous),
which includes SW verging overturned folds (D1) and thrusts (D2), upright folds (D3), extensional faults (D4),
and later faults (D5). These phases of deformation are explained in the context of Variscan tectonics as the
result of the progressive collision between Gondwana and Laurussia. Qualitative unstraining of Variscan
deformation reveals the primary geometry of Ediacaran-Cambrian structures and uncovers the generation of
east verging thrusts as responsible for the primary obduction of the Calzadilla Ophiolite. Restoration of
planar and linear structures associated with this event indicates an Ediacaran, east directed obduction of the
ophiolite, that is, emplacement of the Cadomian fore arc onto inner sections of the northern margin of
Gondwana. According to regional data, the obduction separates two extension-dominated stages in the
tectonic evolution of the African margin of northern Gondwana preserved in southern Europe. Preobduction
extension brought about the onset and widening of fore-arc and back-arc basins in the external part
of the continent, while postobduction extension facilitated the formation of extensional migmatitic domes,
an oceanward migration of back-arc spreading centers across peri-Gondwana, and the eventual opening
of a major basin such as the Rheic Ocean
LHCb pentaquarks in constituent quark models
The recently discovered and states at LHCb have
masses close to the and thresholds,
respectively, which suggest that they may have significant meson-baryon
molecular components. We analyze these states in the framework of a constituent
quark model which has been applied to a wide range of hadronic observables,
being the model parameters, therefore, completely constrained.
The and are studied as molecular states composed
by charmed baryons and open charm mesons. Several bound states with the proper
binding energy are found in the and
channels. We discuss the possible assignments of these states from their decay
widths. Moreover, two more states are predicted, associated with the and thresholds.Comment: 5 pages, 2 table
Possible loss and recovery of Gibbsianness during the stochastic evolution of Gibbs measures
We consider Ising-spin systems starting from an initial Gibbs measure
and evolving under a spin-flip dynamics towards a reversible Gibbs measure
. Both and are assumed to have a finite-range
interaction. We study the Gibbsian character of the measure at time
and show the following: (1) For all and , is Gibbs
for small . (2) If both and have a high or infinite temperature,
then is Gibbs for all . (3) If has a low non-zero
temperature and a zero magnetic field and has a high or infinite
temperature, then is Gibbs for small and non-Gibbs for large
. (4) If has a low non-zero temperature and a non-zero magnetic field
and has a high or infinite temperature, then is Gibbs for
small , non-Gibbs for intermediate , and Gibbs for large . The regime
where has a low or zero temperature and is not small remains open.
This regime presumably allows for many different scenarios
Quark Cluster Model Study of Isospin-Two Dibaryons
Based on a quark cluster model for the non-strange sector that reproduces
reasonably well the nucleon-nucleon system and the excitation of the
isobar, we generate a nucleon- interaction and present the predictions
for the several isospin two channels. The only attractive channels are
and , but not attractive enough to generate a resonance. If a resonance is
artificially generated and is required to have the observed experimental mass,
then our model predicts a width that agrees with the experimental result.Comment: 12 pages, 5 poscript figures available under request. To appear in
Phys. Rev.
Heavy mesons in the Quark Model
Since the discovery of the , the quark model was very successful in
describing the spectrum and properties of heavy mesons including only
components. However since 2003, with the discovery of the , many
states that can not be accommodated on the naive quark model have been
discovered, and they made unavoidable to include higher Fock components on the
heavy meson states. We will give an overview of the success of the quark model
for heavy mesons and point some of the states that are likely to be more
complicated structures such as meson-meson molecules.Comment: Contribution to the Proceedings of the 15th International Workshop on
Meson Physics - MESON201
A family of complex potentials with real spectrum
We consider a two-parameter non hermitean quantum-mechanical hamiltonian that
is invariant under the combined effects of parity and time reversal
transformation. Numerical investigation shows that for some values of the
potential parameters the hamiltonian operator supports real eigenvalues and
localized eigenfunctions. In contrast with other PT symmetric models, which
require special integration paths in the complex plane, our model is integrable
along a line parallel to the real axis.Comment: Six figures and four table
The X(3872) and other possible molecular states
We perform a coupled channel calculation of the and sectors
in the framework of a constituent quark model. The interaction for the
states is obtained using the Resonant Group Method (RGM) and the underlying
quark interaction model. The coupling with the two quark system is performed
using the model. The X(3872) is found as a molecular state with a
sizable component. A comparison with Belle and BaBar data has been
done, finding a good agreement. Other possible molecular molecular states are
discussed.Comment: 5 pages, 5 figures, Proceedings to the Hadron 2009 - XIII
International Conference on Hadron Spectroscopy, Florida State University
(USA
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