On energy-momentum and spin/helicity of quark and gluon fields
Abstract
In special relativity, quantum matter can be classified according to mass-energy and spin. The corresponding field-theoretical notions are the energy-momentum-stress tensor T and the spin angular momentum tensor S. Since each object in physics carries energy and, if fermionic, also spin, the notions of T and S can be spotted in all domains of physics. We discuss the T and S currents in Special Relativity (SR), in General Relativity (GR), and in the Einstein-Cartan theory of gravity (EC). We collect our results in 4 theses: (i) The quark energy-momentum and the quark spin are described correctly by the canonical (Noether) currents T and S, respectively. (ii) The gluon energy-momentum current is described correctly by the (symmetric and gauge invariant) Minkowski type current. Its (Lorentz) spin current vanishes, S = 0. However, it carries helicity of plus or minus one. (iii) GR contradicts thesis (i), but is compatible with thesis (ii). (iv) Within the viable EC-theory, our theses (i) and (ii) are fulfilled and, thus, we favor this gravitational theory.
Keywords
Cite
@article{arxiv.1402.0261,
title = {On energy-momentum and spin/helicity of quark and gluon fields},
author = {Friedrich W. Hehl},
journal= {arXiv preprint arXiv:1402.0261},
year = {2014}
}
Comments
10 pages latex. Invited talk delivered at the XV Workshop on High Energy Spin Physics `DSPIN-13' in Dubna, Russia, 08--12 October 2013