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A detailed analysis of the lowest two moments of the $\phi$ meson spectralfunction in vacuum and nuclear matter is performed. The consistency is examinedbetween the constraints derived from finite energy QCD sum rules and thespectra computed within an improved vector dominance model, incorporating thecoupling of kanonic degrees of freedom with the bare $\phi$ meson. In thevacuum, recent accurate measurements of the $e^+ e^- \to K^+ K^-$ cross sectionallow us to determine the spectral function with high precision. In nuclearmatter, the modification of the spectral function can be described by theinteractions of the kaons from $\phi \rightarrow K\bar{K}$ with the surroundingnuclear medium. This leads primarily to a strong broadening and an asymmetricdeformation of the $\phi$ meson peak structure. We confirm that, both in vacuumand nuclear matter, the zeroth and first moments of the corresponding spectralfunctions satisfy the requirements of the finite energy sum rules to aremarkable degree of accuracy. Limits on the strangeness sigma term of thenucleon are examined in this context. Applying our results to the second momentof the spectrum, we furthermore discuss constraints on four-quark condensatesand the validity of the commonly used ground state saturation approximation.

Phi meson spectral moments and QCD condensates in nuclear matter