778 research outputs found
Chiral Odd Generalized Parton Distributions in Position Space
We report on a calculation of the chiral odd generalized parton distributions
(GPDs) for non-zero skewness in transverse and longitudinal position
spaces by taking Fourier transform with respect to the transverse and
longitudinal momentum transfer respectively using overlaps of light-front wave
functions (LFWFs).Comment: Presented at the 18 th International Spin Physics Symposium,
University of Virginia, Charlottesville, Virginia, USA, October 6-11, 200
Interpretation of the Flavor Dependence of Nucleon Form Factors in a Generalized Parton Distribution Model
We give an interpretation of the and quarks contributions to the
nucleon electromagnetic form factors for values of the four-momentum transfer
in the multi-GeV region where flavor separated data have been recently made
available. The data show, in particular, a suppression of quarks with
respect to quarks at large momentum transfer. %and constant ratios of the
flavor dependent Pauli to Dirac form factors ratios. This trend can be
explained using a reggeized diquark model calculation of generalized parton
distributions, thus providing a correlation between momentum and coordinate
spaces, both of which are necessary in order to interpret the partonic
substructure of the form factors. We extend our discussion to the second
moments of generalized parton distributions which are believed to contribute to
partonic angular momentum.Comment: 22 pages, 19 figures; results and figures added and changed, tables
added, formulae added, major rewriting of tex
First-order symmetric-hyperbolic Einstein equations with arbitrary fixed gauge
We find a one-parameter family of variables which recast the 3+1 Einstein
equations into first-order symmetric-hyperbolic form for any fixed choice of
gauge. Hyperbolicity considerations lead us to a redefinition of the lapse in
terms of an arbitrary factor times a power of the determinant of the 3-metric;
under certain assumptions, the exponent can be chosen arbitrarily, but
positive, with no implication of gauge-fixing.Comment: 5 pages; Latex with Revtex v3.0 macro package and style; to appear in
Phys. Rev. Let
Self-Organizing Maps Algorithm for Parton Distribution Functions Extraction
We describe a new method to extract parton distribution functions from hard
scattering processes based on Self-Organizing Maps. The extension to a larger,
and more complex class of soft matrix elements, including generalized parton
distributions is also discussed.Comment: 6 pages, 3 figures, to be published in the proceedings of ACAT 2011,
14th International Workshop on Advanced Computing and Analysis Techniques in
Physics Researc
CORYNOSOMA AUSTRALE JOHNSTON, 1937 AND C. CETACEUM JOHNSTON & BEST, 1942 (ACANTHOCEPHALA: POLYMORPHIDAE) FROM MARINE MAMMALS AND FISH IN ARGENTINIAN WATERS: ALLOZYME MARKERS AND TAXONOMIC STATUS
Genetic and morphological studies were carried out on acanthocephalans belonging to Corynosoma Luhe, 1904 and referable to the species C. cetaceum Johnston & Best, 1942 and C. australe Johnston, 1937, which were recovered from both definitive and intermediate hosts in Argentinian waters. The aims were to estimate the level of genetic differentiation between the two taxa at any stage of their life-cycle, to provide genetic ( allozyme) markers for their recognition and to analyse the systematic status of both taxa. Acanthocephalans were collected from the stomach and intestine of Arctocephalus australis (Zimmerman), the intestine of Mirounga leonina (Linnaeus) and the stomach of Pontoporia blainvillei Gervais & D'Orbigny (definitive hosts) in Argentinian waters. Alternative alleles at all the 13 enzymatic loci studied were observed for C. australe and C. cetaceum. The specimens from the stomach of both P. blainvillei and A. australis were identified, on the basis of the great number of diagnostic loci found, as C. cetaceum; those from intestine of both A. australis and M. leonina as C. australe. A high level of genetic differentiation (D-Nei= infinity: I-Nei= 0.00) between the two taxa was found, suggesting a generic distinction between the two species. Cystacanths of the two species from the body-cavity of the fish Cynoscion guatucupa (Cuvier) collected from the same geographical area were identified genetically. Morphological patterns, such as the number of hooks and hook rows on the proboscis, the distribution of somatic and genital armature, and other morphometric and meristic differences, in addition to ecological data, enabled the identification of these two species at cystacanth, juvenile and adult stages. However, a number of morphological and morphometric features of the Argentinian material were different to those of C. australe and C. cetaceum described from other regions of the world
Easy as : On the Interpretation of Recent Electroproduction Results
Exclusive electroproduction from nucleons was first suggested by
Ahmad, Goldstein and Liuti for extracting from experimental data the tensor
charge, transversity and other quantities related to chiral odd combinations of
generalized parton distributions. We now explain the details of the process:
{\it i)} the connection between the helicity description and the cartesian
basis; {\it ii)} the dependence on the momentum transfer squared, , and
{\it iii)} the angular momentum, parity, and charge conjugation constraints
( quantum numbers).Comment: 15 pages, 2 figures, some changes in formalism, and text. Introduced
section title
A framework for large-scale relativistic simulations in the characteristic approach
We present a new computational framework (LEO), that enables us to carry out
the very first large-scale, high-resolution computations in the context of the
characteristic approach in numerical relativity. At the analytic level, our
approach is based on a new implementation of the ``eth'' formalism, using a
non-standard representation of the spin-raising and lowering angular operators
in terms of non-conformal coordinates on the sphere; we couple this formalism
to a partially first-order reduction (in the angular variables) of the Einstein
equations. The numerical implementation of our approach supplies the basic
building blocks for a highly parallel, easily extensible numerical code. We
demonstrate the adaptability and excellent scaling of our numerical code by
solving, within our numerical framework, for a scalar field minimally coupled
to gravity (the Einstein-Klein-Gordon problem) in 3-dimensions. The nonlinear
code is globally second-order convergent, and has been extensively tested using
as reference a calibrated code with the same boundary-initial data and radial
marching algorithm. In this context, we show how accurately we can follow
quasi-normal mode ringing. In the linear regime, we show energy conservation
for a number of initial data sets with varying angular structure. A striking
result that arises in this context is the saturation of the flow of energy
through the Schwarzschild radius. As a final calibration check we perform a
large simulation with resolution never achieved before.Comment: RevTeX4, 22 pages, 21 figures, to appear in Phys. Rev.
Genetic evidence of two sibling species within the Contracoecum ogmorhini Johnson & Mawson 1941 complex (Nematoda; Anisakidae) from otariid seals in boreal and austral regions
Genetic variation of Contracaecum ogmorhini (sensu lato) populations from different otariid seals of the northern
and southern hemisphere was studied on the basis of 18 enzyme loci as well as preliminary sequence analysis of
the mitochondrial cyt b gene (260 bp). Samples were collected from Zalophus californianus in the boreal region
and from Arctocephalus pusillus pusillus, A. pusillus doriferus and A. australis from the austral region. Marked
genetic heterogeneity was found between C. ogmorhini (sensu lato) samples from the boreal and austral region,
respectively. Two loci (Mdh-2 and NADHdh) showed fixed differences and a further three loci (Iddh, Mdh-1 and
6Pgdh) were highly differentiated between boreal and austral samples. Their average genetic distance was DNei =
0.36 at isozyme level. At mitochondrial DNA level, an average proportion of nucleotide substitution of 3.7% was
observed. These findings support the existence of two distinct sibling species, for which the names C. ogmorhini
(sensu stricto) and C. margolisi n. sp., respectively, for the austral and boreal taxon, are proposed. A description
for C. margolisi n. sp. is provided. No diagnostic morphological characters have so far been detected; on the other hand, two enzyme loci, Mdh-2 and NADHdh, fully diagnostic between the two species, can be used for the routine identification of males, females and larval stages. Mirounga leonina was found to host C. ogmorhini (s.s.) inmixed infections with C. osculatum (s.l.) (of which C. ogmorhini (s.l.) was in the past considered to be a synonym)
and C. miroungae; no hybrid genotypes were found,confirming the reproductive isolation of these three anisakid species. The hosts and geographical range so far recorded for C. margolisi n. sp. and C. ogmorhini (s.s.) are given
Image distortion in non perturbative gravitational lensing
We introduce the idea of {\it shape parameters} to describe the shape of the
pencil of rays connecting an observer with a source lying on his past
lightcone. On the basis of these shape parameters, we discuss a setting of
image distortion in a generic (exact) spacetime, in the form of three {\it
distortion parameters}. The fundamental tool in our discussion is the use of
geodesic deviation fields along a null geodesic to study how source shapes are
propagated and distorted on the path to an observer. We illustrate this
non-perturbative treatment of image distortion in the case of lensing by a
Schwarzschild black hole. We conclude by showing that there is a
non-perturbative generalization of the use of Fermat's principle in lensing in
the thin-lens approximation.Comment: 22 pages, 6 figures, to appear in Phys. Rev. D (January 2001
A candidate for a background independent formulation of M theory
A class of background independent membrane field theories are studied, and
several properties are discovered which suggest that they may play a role in a
background independent form of M theory. The bulk kinematics of these theories
are described in terms of the conformal blocks of an algebra G on all oriented,
finite genus, two-surfaces. The bulk dynamics is described in terms of causal
histories in which time evolution is specified by giving amplitudes to certain
local changes of the states. Holographic observables are defined which live in
finite dimensional states spaces associated with boundaries in spacetime. We
show here that the natural observables in these boundary state spaces are, when
G is chosen to be Spin(D) or a supersymmetric extension of it, generalizations
of matrix model coordinates in D dimensions. In certain cases the bulk dynamics
can be chosen so the matrix model dynamics is recoverd for the boundary
observables. The bosonic and supersymmetric cases in D=3 and D=9 are studied,
and it is shown that the latter is, in a certain limit, related to the matrix
model formulation of M theory. This correspondence gives rise to a conjecture
concerning a background independent form of M theory in terms of which
excitations of the background independent membrane field theory that correspond
to strings and D0 branes are identified.Comment: Latex 46 pages, 21 figures, new results included which lead to a
modification of the statement of the basic conjecture. Presentation improve
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