On the importance of Lorentz structure in the parton model: target mass corrections, transverse momentum dependence, positivity bounds

Abstract

We show that respecting the underlying Lorentz structure in the parton model has very strong consequences. Failure to insist on the correct Lorentz covariance is responsible for the existence of contradictory results in the literature for the polarized structure function g_2(x), whereas with the correct imposition we are able to derive the Wandzura-Wilczek relation for g_2(x) and the target-mass corrections for polarized deep inelastic scattering without recourse to the operator product expansion. We comment briefly on the problem of threshold behaviour in the presence of target-mass corrections. Careful attention to the Lorentz structure has also profound implications for the structure of the transverse momentum dependent parton densities often used in parton model treatments of hadron production, allowing the k_T dependence to be derived explicitly. It also leads to stronger positivity and Soffer-type bounds than usually utilized for the collinear densities.

RevTeX4, 17 pages, 7 eps figures

References in corpus (7)

• Azimuthal and Single Spin Asymmetries in Hard Scattering Processes
• What can break the Wandzura--Wilczek relation?
• Transverse momentum dependent distribution functions in a covariant parton model approach with quark orbital motion
• Parton distribution functions and quark orbital motion
• Target mass corrections for spin-dependent structure functions in collinear factorization
• Transversity and intrinsic motion of the constituents
• Some Remarks on Methods of QCD Analysis of Polarized DIS Data

Cited by in corpus (20)

• The relation between TMDs and PDFs in the covariant parton model approach
• Next-to leading order analysis of target mass corrections to structure functions and asymmetries
• Modelling the nucleon structure
• Semiinclusive DIS cross sections and spin asymmetries in the quantum statistical parton distributions approach
• Nucleon spin structure functions at NNLO in the presence of target mass corrections and higher twist effects
• Structure of the nucleon at leading and subleading twist in the covariant parton model
• Generalized Cahn effect and parton 3D motion in a covariant approach
• What does kinematical target mass sensitivity in DIS reveal about hadron structure?
• Target mass corrections and higher twist effects in polarized deep-inelastic scattering
• What are the low-$Q$ and large-$x$ boundaries of collinear QCD factorization theorems?
• Proton spin in leading order of the covariant approach
• Lorentz invariance relations and Wandzura-Wilczek approximation
• The problem of kinematic mass corrections for unpolarized semi-inclusive deep inelastic scattering
• New study of the Boer-Mulders function: Implications for the quark and hadron transverse momenta
• Consistency tests for the extraction of the Boer-Mulders and Sivers functions
• Duality of thermal and dynamical descriptions in particle interactions
• Quark-model relations among TMDs in the parton model
• On the role of quark orbital angular momentum in the proton spin
• The QCD evolution of TMD in the covariant approach
• Parton Interpretation and Twist-4 Parton Distributions