87 research outputs found
Twist-3 Effects in Polarized Photon Structure
The polarized photon structure is described by two spin structure functions
and which can be studied in the future polarized ep
or ee colliders. Here we investigate the QCD twist-3 effects in
to the leading order in QCD.Comment: 4 pages, LaTeX2e, 2 eps figures, ws-ijmpa.cls file included, Talk
given at the 3rd Circum-Pan-Pacific Symposium on High Energy Spin Physics,
Beijing, October 8-13, 2001, to appear in the Proceeding
Modified Wandzura-Wilczek Relation with the Nachtmann Variable
If one retains M^2/Q^2 terms in the kinematics, the Nachtmann variable \xi
seems to be more appropriate to describe deep inelastic lepton-nucleon
scattering. Up to the first power of M^2/Q^2, a modified Wandzura-Wilczek
relation with respect to \xi was derived. Kinematical correction factors are
given as functions of \xi and Q^2. A comparison of the modified g_2^WW(\xi) and
original g_2^WW(x) with the most recent g_2 data is shown.Comment: 10 pages, 3 figures, revised version with minor correction
Proton structure corrections to electronic and muonic hydrogen hyperfine splitting
We present a precise determination of the polarizability and other proton
structure dependent contributions to the hydrogen hyperfine splitting, based
heavily on the most recent published data on proton spin dependent structure
functions from the EG1 experiment at the Jefferson Laboratory. As a result, the
total calculated hyperfine splitting now has a standard deviation slightly
under 1 part-per-million, and is about 1 standard deviation away from the
measured value. We also present results for muonic hydrogen hyperfine
splitting, taking care to ensure the compatibility of the recoil and
polarizability terms.Comment: 9 pages, 1 figur
Target Mass Effects in Polarized Virtual Photon Structure Functions
We study target mass effects in the polarized virtual photon structure
functions , in the kinematic
region , where is the mass squared of
the probe (target) photon. We obtain the expressions for and in closed form by inverting the
Nachtmann moments for the twist-2 and twist-3 operators. Numerical analysis
shows that target mass effects appear at large and become sizable near
, the maximal value of , as the ratio
increases. Target mass effects for the sum rules of and
are also discussed.Comment: 24 pages, LaTeX, 9 eps figure
Power Counting in the Soft-Collinear Effective Theory
We describe in some detail the derivation of a power counting formula for the
soft-collinear effective theory (SCET). This formula constrains which operators
are required to correctly describe the infrared at any order in the
Lambda_QCD/Q expansion (lambda expansion). The result assigns a unique
lambda-dimension to graphs in SCET solely from vertices, is gauge independent,
and can be applied independent of the process. For processes with an OPE the
lambda-dimension has a correspondence with dynamical twist.Comment: 12 pages, 1 fig, journal versio
Leading and higher twists in the proton polarized structure function at large Bjorken x
A phenomenological parameterization of the proton polarized structure
function has been developed for x > 0.02 using deep inelastic data up to ~ 50
(GeV/c)**2 as well as available experimental results on both photo- and
electro-production of proton resonances. According to the new parameterization
the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a
zero-crossing point at Q**2 = 0.16 +/- 0.04 (GeV/c)**2. Then, low-order
polarized Nachtmann moments have been estimated and their Q**2-behavior has
been investigated in terms of leading and higher twists for Q**2 > 1
(GeV/c)**2. The leading twist has been treated at NLO in the strong coupling
constant and the effects of higher orders of the perturbative series have been
estimated using soft-gluon resummation techniques. In case of the first moment
higher-twist effects are found to be quite small for Q**2 > 1 (GeV/c)**2, and
the singlet axial charge has been determined to be a0[10 (GeV/c)**2] = 0.16 +/-
0.09. In case of higher order moments, which are sensitive to the large-x
region, higher-twist effects are significantly reduced by the introduction of
soft gluon contributions, but they are still relevant at Q**2 ~ few (GeV/c)**2
at variance with the case of the unpolarized transverse structure function of
the proton. Our finding suggests that spin-dependent correlations among partons
may have more impact than spin-independent ones. As a byproduct, it is also
shown that the Bloom-Gilman local duality is strongly violated in the region of
polarized electroproduction of the Delta(1232) resonance.Comment: revised version to appear in Phys. Rev. D; extended discussion on the
generalized DHG sum rul
Nuclear effects in Deep Inelastic Scattering of polarized electrons off polarized 3He and the neutron spin structure functions
It is shown that the nuclear effects playing a relevant role in Deep
Inelastic Scattering of polarized electrons by polarized He are mainly
those arising from the effective proton and neutron polarizations generated by
the and waves in He. A simple and reliable equation relating the
neutron, , and He, , spin structure functions is proposed. It
is shown that the measurement of the first moment of the He structure
function can provide a significant check of the Bjorken Sum Rule.Comment: 11 pages (revTeX), DFUPG 75/93; 5 (postscript) figures available upon
request from the author
On exotic hybrid meson production in gamma* gamma collisions
We present a theoretical study of exotic hybrid meson (JPC=1-+) production in
photon-photon collisions where one of the photons is deeply virtual, including
twist 2 and twist 3 contributions. We calculate the cross section of this
process which turns out to be large enough to imply sizeable counting rates in
the present high luminosity electron-positron colliders. We emphasize
theimportance of the pi eta decay channel for the detection of the hybrid meson
candidate pi_1(1400) and calculate the cross section and the angular
distribution for pi eta pair production in the unpolarized case. This angular
distribution is a useful tool for disentangling the hybrid meson signal from
the background. Finally, we calculate the single spin asymmetry associated with
one initial longitudinally polarized lepton.Comment: 13 pages, 14 figure
The Small-x Behaviour of the Singlet Polarized Structure Function g_2 in the Double Logarithmic Approximation
The small-x behavior of the singlet contributions to the polarized structure
function g_2(x,Q^2) is calculated in the double-logarithmic approximation of
perturbative QCD. The dominant contribution is due to the gluons which, in
contrast to the unpolarized case, mix with the fermions also in the small-x
domain. We find a power-like growth in 1/x in the odd-signature parts of the
amplitude with the same power as in the singlet function g_1(x,Q^2) at x<< 1.Comment: 20 pages, latex, 3 ps figure
Chiral Quark Model
In this talk I review studies of hadron properties in bosonized chiral quark
models for the quark flavor dynamics. Mesons are constructed from
Bethe--Salpeter equations and baryons emerge as chiral solitons. Such models
require regularization and I show that the two--fold Pauli--Villars
regularization scheme not only fully regularizes the effective action but also
leads the scaling laws for structure functions. For the nucleon structure
functions the present approach serves to determine the regularization
prescription for structure functions whose leading moments are not given by
matrix elements of local operators. Some numerical results are presented for
the spin structure functions.Comment: Talk presented at the workshop QCD 2002, IIT Kanpur, Nov. 2002, 10
pages, proceedings style files include
- …