Axial-Vector and Tensor Spin Polarization and Chiral Restoration in Quark Matter

We study spontaneous the spin polarization of quark matter with flavor SU(2) symmetry at zero temperature in the NJL model. In a relativistic framework, there are two types of spin–spin interactions: axial vector (AV) and tensor (T), which accordingly give rise to different types of spin-polarized materials. When the spin–spin interaction is sufficiently strong, the spin-polarized phase emerges within a specific density region. As the spin–spin interaction becomes stronger, this phase extends over a higher-density region beyond the critical density of chiral restoration in normal quark matter. We show that the spin-polarized phase leads to another kind of spontaneous chiral symmetry breaking phase.