Exploring the impact of strong-force fields on

The unexpected pattern of global spin alignment of vector mesons observed in relativistic heavy-ion collisions for different particle species has posed a serious challenge to theoretical interpretation, as it cannot be explained solely by conventional polarization sources such as vorticity and electromagnetic fields. Fluctuations of strong-force fields may be the key to solving this puzzle. In these proceedings, we review our calculations of the spin density matrix for flavorless vector mesons. The large spin alignment observed for ϕ mesons at lower energies may arise from strong-force fields that polarize the strange quarks and antiquarks, which form polarized mesons via coalescence at hadronization. The strength of the effective ϕ field can be inferred from the experimental data on ϕ-meson spin alignment.