Tensor supercurrent in QCD

Abstract

An external Abelian magnetic field excites in the QCD vacuum a tensor supercurrent that represents the tensor polarization of the chiral condensate. This tensor supercurrent can be deduced from the chiral lagrangian in the presence of anomalies; a similar tensor supercurrent emerges in rotating systems at finite chemical potential. We discuss the microscopic origin of this supercurrent and argue that it screens the instanton--anti-instanton $I\bar{I}$ molecules in the QCD vacuum, similarly to the vector supercurrent screening Abrikosov vortices in a superconductor. A number of possible experimental manifestations of the tensor supercurrent are discussed: {\it i}) spin alignment of axial-vector and vector mesons in heavy ion collisions; {\it ii}) tensor charge of the nucleon; {\it iii}) transversity of quark distributions in polarized nucleons.