  Polarized quarks and antiquarks in high-energy heavy-ion collisions can lead
to the spin alignment of vector mesons formed by quark coalescence. Using the
relativistic spin Boltzmann equation for vector mesons derived from
Kadanoff-Baym equations with an effective quark-meson model for strong
interaction and quark coalescence model for hadronizaton, we calculate the spin
density matrix element $\rho_{00}$ for $\phi$ mesons and show that anisotropies
of local field correlations or fluctuations with respect to the spin
quantization direction lead to $\phi$ meson's spin alignment. We propose that
the local correlation or fluctuation of $\phi$ fields is the dominant mechanism
for the observed the $\phi$ meson's spin alignment and its strength can be
extracted from experimental data as functions of collision energies. The
calculated transverse momentum dependence of $\rho_{00}$ agrees with STAR's
data. We further predict the azimuthal angle dependence of $\rho_{00}$ which
can be tested in future experiments.
