Dynamic versus Static Structure Functions and Novel Diffractive Effects in QCD Page: 2 of 8
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
In the case of the light-cone gauge A+ = 77 -A = 0, one must also consider the final-state
interactions (rescattering) of the (unstruck) s quark. The gluon propagator in light-cone
gauge is inversely proportional to k+. The momentum of the exchanged gluon k+ is of
6(1/v); thus rescattering contributes at leading twist even in light-cone gauge. The net
result is gauge invariant and identical to a color dipole model calculation. The calcula-
tion of the rescattering effects on DIS in Feynman and light-cone gauge through three
loops is given in detail for an Abelian model in ref. [3]. The result shows that the rescat-
tering corrections reduce the magnitude of the DIS cross section in analogy to nuclear
shadowing.
A new understanding of the role of rescattering in deep inelastic scattering has thus
emerged. The multiple scattering of the struck parton via instantaneous interactions
in the target generates dominantly imaginary diffractive amplitudes, giving rise to an
effective "hard pomeron" exchange. The presence of a rapidity gap between the target
and diffractive system requires that the target remnant emerges in a color-singlet state;
this is made possible in any gauge by the soft rescattering. The resulting diffractive
contributions leave the target intact and do not resolve its quark structure; thus there
are contributions to the DIS structure functions which cannot be interpreted as parton
probabilities [3]; the leading-twist contribution to DIS from rescattering of a quark in
the target is a coherent effect which is not included in the light-front wavefunctions
computed in isolation.
Another novel QCD phenomenon involving nuclei is the antishadowing of the nuclear
structure functions which is observed in deep inelastic lepton scattering and other hard
processes. Empirically, one finds RA(x,Q2) = (F2A(x,Q2)/(A/2)F(x,Q2)) > 1 in the
domain 0.1 < x < 0.2; i.e., the measured nuclear structure function (referenced to the
deuteron) is larger than than the scattering on a set of A independent nucleons. Ivan
Schmidt, Jian-Jun Yang, and I [4] have extended the analysis of nuclear shadowing
to the shadowing and antishadowing of all of the electroweak structure functions. We
note that there are also leading-twist diffractive contributions Y*Ni - (qq)Ni arising
from Reggeon exchanges in the t-channel [5]. For example, isospin-non-singlet C =
+ Reggeons contribute to the difference of proton and neutron structure functions,
giving the characteristic Kuti-Weisskopf Fp - Fn - xi aR(0) _ x0.5 behavior at small
x. The x dependence of the structure functions reflects the Regge behavior vaR(O) of
the virtual Compton amplitude at fixed Q2 and t = 0. The phase of the diffractive
amplitude is determined by analyticity and crossing to be proportional to -1 + i for
aR = 0.5, which together with the phase from the Glauber cut, leads to constructive
interference of the diffractive and nondiffractive multi-step nuclear amplitudes. The
nuclear structure function is predicted to be enhanced precisely in the domain 0.1 <
x < 0.2 where antishadowing is empirically observed. The strength of the Reggeon
amplitudes is fixed by the fits to the nucleon structure functions, so there is little model
dependence. Quarks of different flavors will couple to different Reggeons; this leads
to the remarkable prediction that nuclear antishadowing is not universal; it depends on
the quantum numbers of the struck quark. This picture implies substantially different
antishadowing for charged and neutral current reactions, thus affecting the extraction of
the weak-mixing angle Ow. We find that part of the anomalous NuTeV result [6] for Ow
could be due to the non-universality of nuclear antishadowing for charged and neutral
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Brodsky, Stanley J. Dynamic versus Static Structure Functions and Novel Diffractive Effects in QCD, article, November 12, 2008; [Menlo Park, California]. (https://digital.library.unt.edu/ark:/67531/metadc895794/m1/2/: accessed March 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.