Moments of the ϕ meson spectral function in vacuum and in nuclear matter are analyzed, combining a model based on chiral SU(3) effective field theory (with kaonic degrees of freedom) and finite-energy QCD sum rules. For the vacuum we show that the spectral density is strongly constrained by a recent accurate measurement of the e+e-→K+K- cross section. In nuclear matter the ϕ spectrum is modified by interactions of the decay kaons with the surrounding nuclear medium, leading to a significant broadening and an asymmetric deformation of the ϕ meson peak. We demonstrate that both in vacuum and nuclear matter, the first two moments of the spectral function are compatible with finite-energy QCD sum rules. A brief discussion of the next-higher spectral moment involving strange four-quark condensates is also presented.
Gubler, P., & Weise, W. (2015). Moments of ϕ meson spectral functions in vacuum and nuclear matter. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 751, 396–401. https://doi.org/10.1016/j.physletb.2015.10.068