2000/04/27 by A. Harindranath, Harindranath, A., Asmita Mukherjee +3
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #High Energy Physics - Theory (hep-th) #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ph #hep-th
paper · pdf · doi:10.48550/arxiv.hep-th/0004192
22 pages, revtex
arxiv created 2000/04/27 · openalex publication_date 2000/04/27 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
In this work we initiate a systematic investigation of the spin of a composite system in an arbitrary reference frame in QCD. After a brief review of the difficulties one encounters in equal-time quantization, we turn to light-front quantization. We show that, in spite of the complexities, light-front field theory offers a unique opportunity to address the issue of relativistic spin operators in an arbitrary reference frame since boost is kinematical in this formulation. Utilizing this symmetry, we show how to introduce transverse spin operators for massless particles in an arbitrary reference frame in analogy with those for massive particles. Starting from the manifestly gauge invariant, symmetric energy momentum tensor in QCD, we derive expressions for the interaction dependent transverse spin operators \cal Ji (i=1,2) which are responsible for the helicity flip of the nucleon in light-front quantization. In order to construct \cal Ji, first we derive expressions for the transverse rotation operators Fi. In the gauge A+=0, we eliminate the constrained variables. In the completely gauge fixed sector, in terms of the dynamical variables, we show that one can decompose \cal Ji= \cal JiI + \cal JiII + \cal JiIII where only \cal JiI has explicit coordinate (x-, xi) dependence in its integrand. The operators \cal JiII and \cal JiIII arise from the fermionic and bosonic parts respectively of the gauge invariant energy momentum tensor. We discuss the implications of our results.