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تسجيل مستخدم جديدQCD Aspects of the NuTeV Anomaly
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Stefan Kretzer
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The weak mixing angle measured in neutrino scattering differs from the world average of other measurements by about 3 sigma. I discuss QCD corrections of perturbative and nonperturbative (parton structure) origin to the underlying neutrino observables.
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The $s$-$bar{s}$ asymmetry in nucleon sea is an important observable for understanding nucleon structure and strong interaction. There have been many theoretical attempts on this subject and recently on its relation to the NuTeV anomaly. Calculations
with different theoretical frameworks lead to different conclusions. Here assuming a newly proposed penta-quark configuration for the $s$-$bar{s}$ asymmetry in nucleon, we examine its contribution to the NuTeV anomaly, with a result of about $10-20%$.
After some general remarks on non-perturbative QCD I present shortly models which lead to a color-electric flux tube formation. The implications of such a flux tube formation especially on high energy scattering are discussed.
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Consequences of QCD current algebra formulated on a light-like hyperplane are derived for the forward scattering of vector and axial-vector currents on an arbitrary hadronic target. It is shown that current algebra gives rise to a special class of su
m rules that are direct consequences of the independent chiral symmetry that exists at every point on the two-dimensional transverse plane orthogonal to the lightlike direction. These sum rules are obtained by exploiting the closed, infinite-dimensional algebra satisfied by the transverse moments of null-plane axial-vector and vector charge distributions. In the special case of a nucleon target, this procedure leads to the Adler-Weisberger, Gerasimov-Drell-Hearn, Cabbibo-Radicatti and Fubini-Furlan-Rossetti sum rules. Matching to the dispersion-theoretic language which is usually invoked in deriving these sum rules, the moment sum rules are shown to be equivalent to algebraic constraints on forward S-matrix elements in the Regge limit.
A fundamental property of QCD is the presence of the chiral anomaly, which is the primary component of the $pi^0rightarrowgammagamma$ decay amplitude. Based on this anomaly and its small ($simeq$ 4.5%) chiral correction, a firm prediction of the $pi^
0$ lifetime can be used as a test of QCD at confinement scale energies. The interesting experimental and theoretical histories of the $pi^0$ meson are reviewed, from discovery to the present era. Experimental results are in agreement with the theoretical prediction, within the current ($simeq$ 3%) experimental error; however, they are not yet sufficiently precise to test the chiral corrected result, which is a firm QCD prediction and is known to $simeq$ 1% uncertainty. At this level there exist experimental inconsistencies, which require attention. Possible future work to improve the present precision is suggested.
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