376 research outputs found
Leading Chiral Logarithms for Pion Form Factors to Arbitrary Number of Loops
We develop the method of calculation of the leading chiral (infrared)
logarithms to an arbitrary loop order for various form factors of
Nambu-Goldstone bosons. The method is illustrated on example of scalar and
vector form factors in massless 4D O(N+1)/O(N) sigma-model. The analytical
properties of the form factors are derived. The leading chiral (infrared)
logarithms are summed up in the large N limit.Comment: 5 page
Hermes and the spin of the proton
HERMES is a second generation experiment to study the spin structure of the
nucleon, in which measurements of the spin dependent properties of
semi-inclusive deep-inelastic lepton scattering are emphasized. Data have been
accumulated for semi-inclusive pion, kaon, and proton double-spin asymmetries,
as well as for high-p_T hadron pairs, and single-spin azimuthal asymmetries for
pion electroproduction and deep virtual Compton scattering. These results
provide information on the flavor decomposition of the polarized quark
distributions in the nucleon and a first glimpse of the gluon polarization,
while the observation of the azimuthal asymmetries show promise for probing the
tensor spin of the nucleon and isolating the total angular momentum carried by
the quarks.Comment: LaTeX, 21 page
The Ni(n,) cross section measured with DANCE
The neutron capture cross section of the s-process branch nucleus Ni
affects the abundances of other nuclei in its region, especially Cu and
Zn. In order to determine the energy dependent neutron capture cross
section in the astrophysical energy region, an experiment at the Los Alamos
National Laboratory has been performed using the calorimetric 4 BaF
array DANCE. The (n,) cross section of Ni has been determined
relative to the well known Au standard with uncertainties below 15%.
Various Ni resonances have been identified based on the Q-value.
Furthermore, the s-process sensitivity of the new values was analyzed with the
new network calculation tool NETZ.Comment: 11 pages, 13 page
Twist-3 contribution to the amplitude in the Wandzura-Wilczek approximation
We have calculated the Wandzura-Wilczek contribution to the twist-3 part of
amplitude. It describes interaction of the
longitudinally polarized virtual photon with the real one, and it is suppressed
by 1/Q, where is the virtuality of the , as compared to the
twist-2 contribution. We have found that, in the Wandzura-Wilczek
approximation, factorization applies to the twist-3 amplitude.Comment: 13 pages, 4 figure
The dual parametrization for gluon GPDs
We consider the application of the dual parametrization for the case of gluon
GPDs in the nucleon. This provides opportunities for the more flexible modeling
unpolarized gluon GPDs in a nucleon which in particular contain the invaluable
information on the fraction of nucleon spin carried by gluons. We perform the
generalization of Abel transform tomography approach for the case of gluons. We
also discuss the skewness effect in the framework of the dual parametrization.
We strongly suggest to employ the fitting strategies based on the dual
parametrization to extract the information on GPDs from the experimental data.Comment: 37 pages, 2 figure
Angular distributions in hard exclusive production of pion pairs
Using the leading order amplitudes of hard exclusive electroproduction of
pion pairs we have analyzed the angular distribution of the two produced
particles. At leading twist a pion pair can be produced only in an isovector or
an isoscalar state. We show that certain components of the angular distribution
only get contributions from the interference of the I=1 and the (much smaller)
I=0 amplitude. Therefore our predictions prove to be a good probe of isospin
zero pion pair production. We predict effects of a measurable size that could
be observed at experiments like HERMES. We also discuss how hard exclusive pion
pair production can provide us with new information on the effective chiral
Lagrangian.Comment: 17 pages, version to appear in Phys. Rev.
Continuity of generalized parton distributions for the pion virtual Compton scattering
We discuss a consistent treatment of the light-front gauge-boson and meson
wave functions in the analyses of the generalized parton distributions(GPDs)
and the scattering amplitudes in deeply virtual Compton scattering(DVCS) for
the pion. The continuity of the GPDs at the crossover, where the longitudinal
momentum fraction of the probed quark is same with the skewedness parameter,
and the finiteness of the DVCS amplitude are ensured if the same light-front
radial wave function as that of the meson bound state wave function is used for
the gauge boson bound state arising from the pair-creation(or nonvalence)
diagram. The frame-independence of our model calculation is also guaranteed by
the constraint from the sum rule between the GPDs and the form factors.Comment: 14 pages, 9 figures, we (1) changed the title, (2) added references,
(3) discussed the GPD value at the crossover in Sec. III, version to appear
in Phys. Rev.
DVCS amplitude at tree level: Transversality, twist-3, and factorization
We study the virtual Compton amplitude in the generalized Bjorken region (q^2
-> Infinity, t small) in QCD by means of a light-cone expansion of the product
of e.m. currents in string operators in coordinate space. Electromagnetic gauge
invariance (transversality) is maintained by including in addition to the
twist-2 operators 'kinematical' twist-3 operators which appear as total
derivatives of twist-2 operators. The non-forward matrix elements of the
elementary twist-2 operators are parametrized in terms of two-variable spectral
functions (double distributions), from which twist-2 and 3 skewed distributions
are obtained through reduction formulas. Our approach is equivalent to a
Wandzura-Wilczek type approximation for the twist-3 skewed distributions. The
resulting Compton amplitude is manifestly transverse up to terms of order
t/q^2. We find that in this approximation the tensor amplitude for longitudinal
polarization of the virtual photon is finite, while the one for transverse
polarization contains a divergence already at tree level. However, this
divergence has zero projection on the polarization vector of the final photon,
so that the physical helicity amplitudes are finite.Comment: 34 pages, revtex, 1 eps figure included using epsf. Misprints
corrected, one reference adde
Talk the talk, walk the walk: Defining Critical Race Theory in research
Over the last decade there has been a noticeable growth in published works citing Critical Race Theory (CRT). This has led to a growth in interest in the UK of practical research projects utilising CRT as their framework. It is clear that research on 'race' is an emerging topic of study. What is less visible is a debate on how CRT is positioned in relation to methodic practice, substantive theory and epistemological underpinnings. The efficacy of categories of data gathering tools, both traditional and non-traditional is a discussion point here to explore the complexities underpinning decisions to advocate a CRT framework. Notwithstanding intersectional issues, a CRT methodology is recognisable by how philosophical, political and ethical questions are established and maintained in relation to racialised problematics. This paper examines these tensions in establishing CRT methodologies and explores some of the essential criteria for researchers to consider in utilising a CRT framework. © 2012 Copyright Taylor and Francis Group, LLC
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