450 research outputs found
Leading infrared logarithms for sigma-model with fields on arbitrary Riemann manifold
We derive non-linear recursion equation for the leading infrared logarithms
(LL) in four dimensional sigma-model with fields on an arbitrary Riemann
manifold. The derived equation allows one to compute leading infrared
logarithms to essentially unlimited loop order in terms of geometric
characteristics of the Riemann manifold.
We reduce the solution of the SU(oo) principal chiral field in arbitrary
number of dimensions in the LL approximation to the solution of very simple
recursive equation. This result paves a way to the solution of the model in
arbitrary number of dimensions at N-->ooComment: Talk given by MVP at the conference devoted to memory of A.N.
Vasilie
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
Determination of two-photon exchange amplitudes from elastic electron-proton scattering data
Using the available cross section and polarization data for elastic
electron-proton scattering, we provide an extraction of the two-photon exchange
amplitudes at a common value of four-momentum transfer, around Q^2 = 2.5 GeV^2.
This analysis also predicts the e^+ p / e^- p elastic scattering cross section
ratio, which will be measured by forthcoming experiments.Comment: 4 pages, 5 figures, updated error analysi
Light-Cone Wavefunction Representation of Deeply Virtual Compton Scattering
We give a complete representation of virtual Compton scattering at large initial photon virtuality and small momentum
transfer squared in terms of the light-cone wavefunctions of the target
proton. We verify the identities between the skewed parton distributions
and which appear in deeply virtual Compton
scattering and the corresponding integrands of the Dirac and Pauli form factors
and and the gravitational form factors and
for each quark and anti-quark constituent. We illustrate the general
formalism for the case of deeply virtual Compton scattering on the quantum
fluctuations of a fermion in quantum electrodynamics at one loop.Comment: References added and minor revisions made in text. Version to appear
in Nucl. Phys.
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 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
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