Holographic spin alignment for vector mesons

We develop a general framework for studying the spin alignment ρ₀₀ for flavorless vector mesons by using the gauge/gravity duality. Focusing on the dilepton production through vector meson decay, we derive the relation between production rates at each spin channel and meson's spectral function, which can be evaluated by holographic models for a strongly coupled system. As examples, we study ρ₀₀ for J/ψ and φ mesons, induced by the relative motion to a thermal background, within the soft-wall model. We show that ρ₀₀ in the helicity frame for J/ψ and φ mesons have positive and negative deviations from 1/3 at $T=150$ MeV, respectively, which consequently leads to different properties for their global spin alignments.