18 research outputs found
Analysis of CLAS data on double charge pion electroproduction
Recent developments in phenomenological analysis of the CLAS data on 2
electroproduction are presented. The contributions from isobar channels and
, electrocouplings at from 0.25 to 0.6
GeV were determined from the analysis of comprehensive data on differential
and fully integrated 2 cross sections. Experiment Numbers: E94-005 Group:
Hall BComment: Paper compiled for NSTAR2007 meetin
Vector- and Pseudoscalar-baryon coupled channel systems
In this manuscript, I will report the details of our recent work on the
vector meson-baryon (VB) interaction, which we studied with the motivation of
finding dynamical generation of resonances in the corresponding systems. We
started our study by building a formalism based on the hidden local symmetry
and calculating the leading order contributions to the scattering equations by
summing the diagrams with: (a) a vector meson exchange in the t-channel (b) an
octet baryon exchange in the s-, u-channels and (c) a contact interaction
arising from the part of the vector meson-baryon Lagrangian which is related to
the anomalous magnetic moment of the baryons. We find the contribution from all
these sources, except the s-channel, to be important. The amplitudes obtained
by solving the coupled channel Bethe-Salpeter equations for the systems with
total strangeness zero, show generation of one isospin 3/2, spin 1/2 resonance
and three isospin 1/2 resonances: two with spin 3/2 and one with spin 1/2. We
identify these resonances with (1900) , (2080) ,
(1700) , and (2090) , respectively.
We have further extended our study by including pseudoscalar meson-baryon
(PB) as the coupled channels of VB systems. For this, we obtain the PB
VB amplitudes by using the Kroll-Ruddermann term where,
considering the vector meson dominance phenomena, the photon is replaced by a
vector meson. The calculations done within this formalism reveal a very strong
coupling of the VB channels to the low-lying resonances like (1405)
and (1670), which can have important implications on certain reactions
producing them. In addition to this, we find that the effect of coupling the
higher mass states to the lighter channels is not restricted to increasing the
width of those states, it can be far more strong.Comment: Proceedings of the "DAE-BRNS Workshop on Hadron Physics" held in
Mumbai, India during October 31-November 04, 201
Proton strangeness form factors in (4,1) clustering configurations
We reexamine a recent result within a nonrelativistic constituent quark model
(NRCQM) which maintains that the uuds\bar s component in the proton has its
uuds subsystem in P state, with its \bar s in S state (configuration I). When
the result are corrected, contrary to the previous result, we find that all the
empirical signs of the form factors data can be described by the lowest-lying
uuds\bar s configuration with \bar s in P state that has its uuds subsystem in
state (configuration II). Further, it is also found that the removal of the
center-of-mass (CM) motion of the clusters will enhance the contributions of
the transition current considerably. We also show that a reasonable description
of the existing form factors data can be obtained with a very small probability
P_{s\bar s}=0.025% for the uuds\bar s component. We further see that the
agreement of our prediction with the data for G_A^s at low-q^2 region can be
markedly improved by a small admixture of configuration I. It is also found
that by not removing CM motion, P_{s\bar s} would be overestimated by about a
factor of four in the case when transition dominates over direct currents.
Then, we also study the consequence of a recent estimate reached from analyzing
the existing data on quark distributions that P_{s\bar s} lies between 2.4-2.9%
which would lead to a large size for the five-quark (5q) system, as well as a
small bump in both G^s_E+\eta G^s_M and G^s_E in the region of q^2 =< 0.1
GeV^2.Comment: Prepared for The Fifth Asia-Pacific Conference on Few-Body Problems
in Physics 2011 in Seoul, South Korea, 22-26 August 201
Inter-planar coupling dependent magnetoresistivity in high purity layered metals
The magnetic field-induced changes in the conductivity of metals are the
subject of intense interest, both for revealing new phenomena and as a valuable
tool for determining their Fermi surface. Here, we report a hitherto unobserved
magnetoresistive effect in ultra-clean layered metals, namely a negative
longitudinal magnetoresistance that is capable of overcoming their very
pronounced orbital one. This effect is correlated with the inter-layer coupling
disappearing for fields applied along the so-called Yamaji angles where the
inter-layer coupling vanishes. Therefore, it is intrinsically associated with
the Fermi points in the field-induced quasi-one-dimensional electronic
dispersion, implying that it results from the axial anomaly among these Fermi
points. In its original formulation, the anomaly is predicted to violate
separate number conservation laws for left- and right-handed chiral- (e.g.
Weyl) fermions. Its observation in PdCoO, PtCoO and SrRuO
suggests that the anomaly affects the transport of clean conductors,
particularly near the quantum limit.Comment: Nature Communications (in press
Electromagnetic Meson Production in the Nucleon Resonance Region
Recent experimental and theoretical advances in investigating electromagnetic
meson production reactions in the nucleon resonance region are reviewed.Comment: 75 pages, 42 figure
Magnetic Frustration Driven by Itinerancy in Spinel CoV2O4
Localized spins and itinerant electrons rarely coexist in geometrically-frustrated spinel lattices. They exhibit a complex interplay between localized spins and itinerant electrons. In this paper, we study the origin of the unusual spin structure of the spinel CoV2O4, which stands at the crossover from insulating to itinerant behavior using the first principle calculation and neutron diffraction measurement. In contrast to the expected paramagnetism, localized spins supported by enhanced exchange couplings are frustrated by the effects of delocalized electrons. This frustration produces a non-collinear spin state even without orbital orderings and may be responsible for macroscopic spin-glass behavior. Competing phases can be uncovered by external perturbations such as pressure or magnetic field, which enhances the frustration