An outstanding problem exists in nuclear physics for a long time is the so-called spin crisis problem. Now physicists realize that it is necessary to decompose the gauge potential into physical part and vacuum part in order to solve this problem. However, up to now, it is still unclear for people on how to decompose it exactly.

Researchers in Institute of Modern Physics, Chinese Academy of Sciences (IMP) and their collaborators from Uzbekistan National University offered a new approach to decompose the gauge potential, which directly related to the helicity of nucleons.

A non-uniqueness problem of gauge invariant separation of quark and gluon contributions to nucleon spin is considered. The study shows that there is a wide number of gauge invariant spin decompositions, and each of them reduces to the canonical one in a special gauge. A class of physical gauge equivalent nucleon spin decompositions is selected by requirements of consistence with helicity notion described within the E(2) little group representation theory and with the gluon helicity Δg measured in the experiment.

The work was published in: Eur. Phys. J. A 48 (2012) 91

The papers can be found on the webpage:  http://link.springer.com/article/10.1140%2Fepja%2Fi2012-12091-8