Year: 2026
Type: preprint
Abstract: Holographic predictions for vector meson spin alignment at finite density have been limited by how the chemical potential is implemented. Existing models use a baryon chemical potential and report that the alignment is insensitive to it, while zero-density benchmarks do not address the geometric deformation. We address this limitation by using a charged AdS black-hole background with a quark chemical potential and solving the coupled bulk vector equations with infalling horizon conditions. The zero-density limit reproduces previous results of Sheng et al. [Phys. Rev. D 110, 056047 (2024)]. At \(T=0.15~\mathrm{GeV}\), the \(J/ψ\) spectral function has a resonance peak at \(μ=0\) that lowers and broadens with increasing \(μ\), whereas the \(ϕ\) spectral function shows no pronounced peak. In the helicity frame, \(ρ_{00}\) deviates positively from \(1/3\) for the \(J/ψ\) and negatively for the \(ϕ\). The density response is more visible in our setup than the weak baryon chemical potential sensitivity reported in a four-flavor soft-wall model. This difference illustrates the model dependence of the density response: it is controlled by the chemical potential normalization. We identify the presence of the resonance peak and the signs of the helicity deviations as robust qualitative features, and treat the numerical shifts of \(ρ_{00}\) as model-dependent estimates.
Source: arXiv (Cornell University)
Authors: Wang, Fei, Zhang, Zi-qiang
Institution: China University of Geosciences
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7206211218