22 research outputs found
Radiative corrections to the structure functions and sum rules in polarized DIS
The one-loop NLO radiative corrections to the observables in polarized DIS
using assumption that a quark is an essential massive particle are considered.
If compared with classical QCD formulae the obtained results are identical for
the unpolarized and different for polarized sum rules, that can be explained as
the influence of the finite quark mass effects on NLO QCD corrections. The
explicit expression for one-loop NLO QCD contribution to the structure function
g_2 is presented.Comment: 6 pages,1 figure. Talk given at the International Workshop "Symmetry
And Spin" - PRAHA-SPIN'9
Gluon Spin in the Nucleon
We study the operator description of the gluon spin contribution ()
to the nucleon's spin as it is measured in deep inelastic processes.
can be related to the forward matrix element of a local gluon operator in
gauge. In quark models the nucleon contains ambient color electric and
magnetic fields. The latter are thought to be responsible for spin splittings
among the light baryons. We show that these fields give rise to a significant
{\it negative\/} contribution to at the quark model renormalization
scale, . The non-Abelian character of QCD is responsible for the sign
of . In a generic non-relativistic quark model , in the bag model
. These correspond to
and at .Comment: 12 pages in REVTeX. The paper has been entirely revise
Errors in Lattice Extractions of alpha_s Due to Use of Unphysical Pion Masses
We investigate the errors due to the use of unphysical values of light quark
masses in lattice extractions of . A functional form for the pion
mass dependence of the quarkonium mass splittings () is given as an
expansion in and , where is the
quarkonium Bohr radius. We find that, to lowest order,, where the scale of is given by . To order
there are four unknown coefficients, however, utilizing multipole and
operator product expansions, symmetry arguments eliminate one of the four
unknowns. Using the central values for the lattice spacings which were
extracted using two different, unphysical values for the pion mass, we find
that the errors introduced by extrapolating to the physical regime are
comparable to the errors quoted due to other sources. Extrapolation to physical
values of the pion mass {\it increases} the value of , bringing
its value closer to the high energy extractions.Comment: Version to appear in PLB, with extended discussion and numbers for
intermediate values of the pion mas
QCD at high energy (experiments)
Recent measurements of QCD interactions involving large momentum transfers
are reviewed. The status of measurements of the strong coupling constant is
summarised. Recent developments in the measurement and interpretation of deep
inelastic scattering, proton-anti-proton collisions and two-photon processes
are discussed. While QCD at next-to-leading order gives a qualitative
description of many processes, next-to-NLO calculations are now required to
allow quantitative information to be extracted from hadron-initiated multijet
data. This is illustrated by a discussion of recent data on the photoproduction
of dijet events at HERA.Comment: Talk presented at the International Conference on High
Energy Physics, Amsterdam, 24-31 July 2002. 18 pages, 30 figure
The Proton Spin in the Chiral Bag Model : Casimir Contribution and Cheshire Cat Principle
The flavor singlet axial charge has been a source of study in the last years
due to its relation to the so called {\it Proton Spin Problem}. The relevant
flavor singlet axial current is anomalous, i.e., its divergence contains a
piece which is the celebrated anomaly. This anomaly is intimately
associated with the meson, which gets its mass from it. When the
gauge degrees of freedom of QCD are confined within a volume as is presently
understood, the anomaly is known to induce color anomaly leading to
"leakage" of the color out of the confined volume (or bag). For consistency of
the theory, this anomaly should be canceled by a boundary term. This ``color
boundary term" inherits part or most of the dynamics of the volume (i.e., QCD).
In this paper, we exploit this mapping of the volume to the surafce via the
color boundary condition to perform a complete analysis of the flavor singlet
axial charge in the chiral bag model using the Cheshire Cat Principle. This
enables us to obtain the hitherto missing piece in the axial charge associated
with the gluon Casimir energies. The result is that the flavor singlet axial
charge is small independent of the confinement (bag) size ranging from the
skyrmion picture to the MIT bag picture, thereby confirming the (albeit
approximate) Cheshire Cat phenomenon.Comment: 18 pages, 6 figure
A texture of neutrino mass matrix in view of recent neutrino experimental results
In view of recent neutrino experimental results such as SNO, Super-Kamiokande
(SK), CHOOZ and neutrinoless double beta decay , we
consider a texture of neutrino mass matrix which contains three parameters in
order to explain those neutrino experimental results. We have first fitted
parameters in a model independent way with solar and atmospheric neutrino mass
squared differences and solar neutrino mixing angle which satisfy LMA solution.
The maximal value of atmospheric neutrino mixing angle comes out naturally in
the present texture. Most interestingly, fitted parameters of the neutrino mass
matrix considered here also marginally satisfy recent limit on effective
Majorana neutrino mass obtained from neutrinoless double beta decay experiment.
We further demonstrate an explicit model which gives rise to the texture
investigated by considering an gauge group with two
extra real scalar singlets and discrete symmetry. Majorana
neutrino masses are generated through higher dimensional operators at the scale
. We have estimated the scales at which singlets get VEV's and M by
comparing with the best fitted results obtained in the present work.Comment: Journal Ref.: Phys. Rev. D66, 053004 (2002
What We Can Learn About Nucleon Spin Structure From Recent Data
We have used recent polarized deep-inelastic scattering data from CERN and
SLAC to extract information about nucleon spin structure. We find that the SMC
proton data, the E142 neutron data and the deuteron data from SMC and E143 give
different results for fractions of the spin carried by each of the
constituents. These appear to lead to two different and incompatible models for
the polarized strange sea. The polarized gluon distribution occuring in the
gluon anomaly does not have to be large in order to be consistent with either
set of experimental data. However, it appears that the discrepancies in the
implications of these data cannot be resolved with any simple theoretical
arguments. We conclude that more experiments must be performed in order to
adequately determine the fraction of spin carried by each of the nucleon
constituents.Comment: 23 page