Transversity from first principles in QCD

Brodsky, S. J. (2012) Transversity from first principles in QCD. Il nuovo cimento C, 35 (2). pp. 339-348. ISSN 1826-9885

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Transversity observables, such as the T-odd Sivers single-spin asymmetry measured in deep inelastic lepton scattering on polarized protons and the distributions which are measured in deeply virtual Compton scattering, provide important constraints on the fundamental quark and gluon structure of the proton. In this talk I discuss the challenge of computing these observables from first principles; i.e.; quantum chromodynamics, itself. A key step is the determination of the frame-independent light-front wave functions (LFWFs) of hadrons—the QCD eigensolutions which are analogs of the Schr¨odinger wave functions of atomic physics. The lensing effects of initial-state and final-state interactions, acting on LFWFs with different orbital angular momentum, lead to T-odd transversity observables such as the Sivers, Collins, and Boer-Mulders distributions. The lensing effect also leads to leading-twist phenomena which break leading-twist factorization such as the breakdown of the Lam-Tung relation in Drell-Yan reactions. A similar rescattering mechanism also leads to diffractive deep inelastic scattering, as well as nuclear shadowing and non-universal antishadowing. It is thus important to distinguish “static” structure functions, the probability distributions computed the target hadron’s light-front wave functions, versus “dynamical” structure functions which include the effects of initial- and final-state rescattering. I also discuss related effects such as the J = 0 fixed pole contribution which appears in the real part of the virtual Compton amplitude. AdS/QCD, together with “Light-Front Holography”, provides a simple Lorentz-invariant color-confining approximation to QCD which is successful in accounting for light-quark meson and baryon spectroscopy as well as hadronic LFWFs.

Item Type: Article
Uncontrolled Keywords: Quantum chromodynamics ; Other nonperturbative calculations ; Factorization ; Polarization in interactions and scattering
Subjects: 500 Scienze naturali e Matematica > 530 Fisica
Depositing User: Marina Spanti
Date Deposited: 19 Apr 2020 14:56
Last Modified: 19 Apr 2020 14:56

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