Spin Alignment of Vector Mesons Induced by Local Spin Density Fluctuations

We propose a novel mechanism that the spin alignment of vector meson φ and K*0 in most central heavy ion collisions is induced by intrinsic QCD dynamics without external vortical/ magnetic fields. The local spin density fluctuation of quarks due to the axial-vector and tensor interactions between quarks can induce the spin alignments of vector meson. It is found that axial-vector interaction results in ρ₀₀<1/3 for the spin alignment of φ meson, while tensor interaction results in ρ₀₀>1/3. We argue that the spin alignment of K*0 due to the spin density fluctuation from flavor-mixing would be a signature or hint of instanton.