Holographic spin alignment of vector mesons in a spinning black-hole background

Abstract

Holographic predictions for vector-meson spin alignment are difficult to compare between charmonium and light vector mesons, as the two sectors are typically treated in different rotating backgrounds and spectral prescriptions. Consequently, it remains unclear whether a single rotating medium can generate the opposite polarization preferences observed in data. We address this by placing \(J/ψ\) and \(ϕ\) in one soft-wall model on the planar limit of a five-dimensional equal-spin Myers--Perry (MP) AdS black hole, computing spectral functions and spin alignment within the same current-correlator framework; the nonrotating results of Sheng et al. [Phys. Rev. D 110, 056047 (2024)] are recovered at \(a=0\). At \(T=0.15~\mathrm{GeV}\), \(J/ψ\) retains a clear resonance peak, whereas \(ϕ\) shows no narrow peak and instead behaves as a broad distribution consistent with unstable \(s\bar{s}\) pairs. For \(J/ψ\) along \(z\), rotation enhances the positive deviation of \(ρ_{00}^{h}\) from \(1/3\) at low and intermediate momenta but suppresses it at high momenta; along \(x\), the effect is small. For \(ϕ\), rotation enhances the negative deviation, more along \(z\) than along \(x\). The opposite helicity-frame signs and the opposing azimuthal and rapidity trends of the global alignment provide a reference for interpreting data: trends inconsistent with these would challenge the simplest single homogeneous rotating-medium interpretation. We distinguish model-dependent numerical details from qualitative features stable within this model class.