73 research outputs found
Bjorken sum rule at low Q^2
A description of the generalized Gerasimov-Drell-Hearn sum rules for proton
and neutron is suggested, using their relation to the Bjorken sum rule. The
results support an earlier conjecture, that the structure function g_T features
a smooth Q^2-dependence, while the structure function g_2 is changing rapidly,
due to the elastic contribution to the Burkhardt-Cottingham sum rule. A
possible violation of this later sum rule is briefly discussed.Comment: 8 pages, 2 eps figure
Experimental determination of the effective strong coupling constant
We present a first attempt to experimentally extract an effective strong
coupling constant that we define to be a low Q2 extension of a previous
definition by S. Brodsky et al. following an initial work of G. Grunberg. Using
Jefferson Lab data and sum rules, we establish its Q2-behavior over the
complete Q2-range. The result is compared to effective coupling constants
inferred from different processes and to calculations based on Schwinger-Dyson
equations, hadron spectroscopy or lattice QCD. Although the connection between
the experimentally extracted effective coupling constants and the calculations
is not established it is interesting to note that their behaviors are similar.Comment: Published in Physics Letters B 650 4 24
Q^2-Dependence of the Proton's G_1 Structure Function Sum Rule
We study the variation of the first moment of the nucleon's
spin-dependent structure function . As the moment is
determined by the low energy theorem for Compton scattering. In the
deep-inelastic region the moment is calculated using twist expansion to order
. Based on these limits, we construct a formula which smoothly
interpolates between the two regions.Comment: (revised), 8 pages in REVTEX, 1 figure, MIT-CTP-223
Higher moments of nucleon spin structure functions in heavy baryon chiral perturbation theory and in a resonance model
The third moment of the twist-3 part of the nucleon spin structure
function is generalized to arbitrary momentum transfer and is
evaluated in heavy baryon chiral perturbation theory (HBChPT) up to order
and in a unitary isobar model (MAID). We show how to link
as well as higher moments of the nucleon spin structure functions
and to nucleon spin polarizabilities. We compare our results with the
most recent experimental data, and find a good description of these available
data within the unitary isobar model. We proceed to extract the twist-4 matrix
element which appears in the suppressed term in the twist
expansion of the spin structure function for proton and neutron.Comment: 30 pages, 7 figure
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