3,019 research outputs found
Dispersion Theory in Electromagnetic Interactions
We review various applications of dispersion relations (DRs) to the
electromagnetic structure of hadrons. We discuss the way DRs allow one to
extract information on hadron structure constants by connecting information
from complementary scattering processes. We consider the real and virtual
Compton scattering processes off the proton, and summarize recent advances in
the DR analysis of experimental data to extract the proton polarizabilities, in
comparison with alternative studies based on chiral effective field theories.
We discuss a multipole analysis of real Compton scattering data, along with a
DR fit of the energy-dependent dynamical polarizabilities. Furthermore, we
review new sum rules for the double-virtual Compton scattering process off the
proton, which allow for model independent relations between polarizabilities in
real and virtual Compton scattering, and moments of nucleon structure
functions. The information on the double-virtual Compton scattering is used to
predict and constrain the polarizability corrections to muonic hydrogen
spectroscopy.Comment: preprint version of a review to appear in Ann. Rev. Nucl. Part. Sci.
68 (2018
Constrained annealing for spin glasses
The quenched free energy of spin glasses is estimated by means of annealed
averages where the frustration is constrained to its average value. We discuss
the case of d-dimensional Ising models with random nearest neighbour coupling,
and we introduce a new method to obtain constrained annealed averages without
recurring to Lagrange multipliers. It requires to perform quenched averages
either on small volumes in an analytic way, or on finite size strips via
products of random transfer matrices. We thus give a sequence of converging
lower bounds for the quenched free energy of 2d spin glasses.Comment: plane TeX file,24 pages. 6 figures may be requested to Paladin at
vxscaq.aquila.infn.i
Dispersive evaluation of the D-term form factor in deeply virtual Compton scattering
We present a dispersive representation of the D-term form factor for hard
exclusive reactions, using unsubtracted -channel dispersion relations. The
-channel unitarity relation is saturated with the contribution of two-pion
intermediate states, using the two-pion distributions amplitude for the
subprocess and reconstructing the
subprocess from available information on
pion-nucleon partial-wave helicity amplitudes. Results for the D-term form
factor as function of as well as at are discussed in comparison with
available model predictions and phenomenological parametrizations.Comment: 8 pages, 3 figures; improved presentation of the results; version to
appear in Phys. Lett.
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Estimating Residual Faults from Code Coverage
Many reliability prediction techniques require an estimate for the number of residual faults. In this paper, a new theory is developed for using test coverage to estimate the number of residual faults. This theory is applied to a specific example with known faults and the results agree well with the theory. The theory is used to justify the use of linear extrapolation to estimate residual faults. It is also shown that it is important to establish the amount of unreachable code in order to make a realistic residual fault estimate
Chiral-odd generalized parton distributions in constituent quark models
We derive the overlap representation of chiral-odd generalized parton
distributions using the Fock-state decomposition in the transverse-spin basis.
This formalism is applied to the case of light-cone wave functions in a
constituent quark model. Numerical results for the four chiral-odd generalized
parton distributions at the hadronic scale are shown in different kinematics.
In the forward limit we derive the transversity distribution, the tensor charge
and the angular momentum sum rule for quarks with transverse polarization in an
unpolarized nucleon.Comment: 23 pages, 7 figures; one reference added and one formula corrected;
conclusions and discussions unchange
Chiral-Odd Generalized Parton Distributions, Transversity and Double Transverse-Spin Asymmetry in Drell-Yan Dilepton Production
Within the framework of light-cone quantization we derive the overlap
representation of generalized parton distributions for transversely polarized
quarks using the Fock-state decomposition in the transverse-spin basis. We
apply this formalism to the case of light-cone wave functions in a constituent
quark model giving numerical results for the four chiral-odd generalized parton
distributions in a region where they describe the emission and reabsorption of
a quark by the nucleon. With the transversity distribution obtained in the
forward limit of the generalized distribution, we provide some predictions for
the double transverse-spin asymmetry in Drell-Yan dilepton production in the
kinematics of the PAX experiment.Comment: 8 pages, 4 figures. To appear in the Proceedings of the "XI
Conference on Problems in Theoretical Nuclear Physics", Cortona, Italy, 11-14
October 200
Light-Front Densities for Transversely Polarized Hadrons
We discuss the recent interpretation of quark distribution functions in the
plane transverse to the light-cone direction. Such a mapping is model
independent and allows one to build multidimensional pictures of the hadron and
to develop a semi-classical intuition of the quark dynamics. We comment briefly
the results obtained from the Form Factors of the nucleon. A generalization to
a target with arbitrary spin led to a set of preferred values for the
electromagnetic coupling characterizing structureless particles. Generalized
polarizabilities can also be interpreted in that frame as the distortion of the
charge densities due to an external electromagnetic field. Finally, we present
preliminary results for the Generalized Transverse-Momentum dependent
Distributions which encode in principle the most complete information about
quark distributions.Comment: 8 pages, 2 figures, 1 table; contribution to the proceedings of "The
4th Workshop on Exclusive Reactions at High Momentum Transfer", Jefferson
Lab., May 18-21, 201
Chiral-Odd Generalized Parton Distributions and Transversity in Light-Front Constituent Quark Models
We present the general framework to calculate chiral-odd generalized parton
distributions in the overlap representation using the Fock-state decomposition
in the transverse spin basis. In the forward limit we derive the transversity
distribution, the tensor charge and the angular momentum sum rule for quarks
with transverse polarization in an unpolarized nucleon. Numerical results are
obtained by applying the formalism to the case of light-cone wavefunctions of
constituent quark models.Comment: 8 pages, 3 figures. Invited talk at the "Advanced Studies Institute
on SYMMETRIES AND SPIN" (SPIN-Praha-2006), 19-26 July, 2006, Prague. To be
pubblished in Czechoslovak Journal of Physics. Some references adde
Two-photon exchange contribution to elastic -proton scattering: Full dispersive treatment of states and comparison with data
We evaluate the two-photon exchange correction to the elastic electron-proton
scattering cross section within a dispersive framework. Besides the elastic
contribution, we account for all intermediate state contributions using
the phenomenological MAID fit as an input. We develop a novel method for the
analytical continuation of the two-photon exchange amplitudes into the
unphysical region and generalize our previous work to the momentum transfer
region . We
compare our results with recent OLYMPUS, CLAS and VEPP-3 data as well as with
empirical fits and estimates in the forward angular region.Comment: 43 pages, 21 figures, version published in Phys. Rev. D 96, 096001
(2017
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