Based on an effective Lagrangian which combines chiral SU(3) dynamics with vector meson dominance, we have developed a model for the forward vector mesonnucleon scattering amplitudes. We use this as an input to calculate the low energy part of the current-current correlation function in nuclear matter. Its spectrum enters directly in the "left hand side" of QCD sum rules. For the isovector channel we find a significant enhancement of the in-medium spectral density below the ρ resonance while the ρ meson mass itself changes only slightly. The situation is different in the isoscalar channel, where the mass and peak position of the ω meson move downward while its width increases less drastically than in the ρ meson case. For the φ meson we find almost no mass shift; the width of the peak broadens moderately. We observe a remarkable degree of consistency with the operator product expansion of QCD sum rules in all three channels. We point out, however, that these results cannot simply be interpreted, as commonly done, in terms of a universal rescaling of vector meson masses in matter.

An improved update of the structure and decays of ρ 0 , ω and φ mesons based on a chiral SU(3) Lagrangian, including anomaly terms is presented. We demonstrate that a consistent and quantitatively successful description of both pion and kaon electromagnetic form factors can be achieved. We also discuss the e + e − → π + π 0 π − cross section, the Dalitz decay ω → π 0 µ + µ − and aspects of ρ 0 ω and ωφ mixing. Relations to previous versions of the Vector Meson Dominance model will be examined.

The vacuum spectrum of the φ-meson is characterized by its decay into KK. Modifications of the KK-loops in baryonic matter change this spectrum. We calculate these in-medium modifications taking both s-and p-wave kaon-nucleon interactions into account. We use results of the in-medium K and K spectra determined previously from a coupled channel approach based on a chiral effective Lagrangian. Altogether we find a very small shift of the φ meson mass, by less than 10 MeV at normal nuclear matter density ρ 0 . The in-medium decay width of the φ meson increases such that its life time at ρ = ρ 0 is reduced to less than 5 fm/c. It should therefore be possible to observe medium effects in reactions such as π − p → φn in heavy nuclei, where the φ meson can be produced with small momentum.

We investigate the masses of the lowest cc states, the J͞c and h c , in nuclear matter using QCD sum rules. Up to dimension four, the differences between the operator product expansions in vacuum and in medium arise from the density-dependent change in the gluon condensate and from a new contribution proportional to the nucleon expectation value of the twist-2 gluon operator. Both terms together give an attractive shift of about 5 -10 MeV to the J͞c and h c masses in nuclear matter.[S0031-9007(99)09014-6] PACS numbers: 14.40. Gx, 11.55.Hx, 24.85. + p Investigating the behavior of heavy quark systems in a nuclear medium is of great interest, for several reasons. First, the ongoing discussion of J͞c suppression in ultrarelativisitic heavy-ion collisions as a possible quarkgluon plasma signal requires detailed knowledge about the in-medium interactions of the J͞c under "normal," nonplasma conditions. Furthermore, as Brodsky et al. [1] pointed out, multigluon exchange can lead to an attractive potential between a cc meson and a nucleon, such that, for example, the h c could form bound states even with light nuclei. In more recent calculations the estimated charmonium binding energy in nuclear systems was found to be of the order of 10 MeV [2][3][4][5].In the present paper we study the in-medium behavior of the J͞c and h c using QCD sum rules [6]. The QCD sum rule approach connects the spectral density of a given current correlation function via a dispersion relation with the QCD operator product expansion (OPE). Inmedium QCD sum rules have so far been applied only for light quark systems, in order to study possible shifts of the in-medium masses of nucleons [7-9] and vector mesons [10]. Such calculations suffer from uncertainties, e.g., due to assumptions about factorization of fourquark condensates which may not be justified. As we shall see, in-medium QCD sum rules applied to heavy quark systems are expected to be more reliable. Up to dimension four, the order to which the vacuum sum rules for hadrons involving heavy quarks are commonly expanded, all condensate parameters are quite well known and there are no ambiguities in the OPE. We also find that uncertainties caused by possibly large hadronic inmedium decay widths are much smaller than for lightquark systems.Our starting point is the time ordered current-current correlation function of two heavy quark currents in nuclear matter (n.m.), P͑v,q͒ i Z d 4 x e iq?x ͗jT ͓ j͑x͒j͑0͔͒j͘ n.m. . (1) Here q ͑v, q͒, and j͘ n.m. is the ground state of nuclear matter which we take to be at rest. For the J͞c we take the vector current j V m cg m c and for the h c , we use the pseudoscalar current j P icg 5 c. In the region of large and positive Q 2 q 2 2 v 2 we can express the correlation function through an operator product expansion (short distance expansion) [11] and write the left hand side of Eq. (1) asHere the O n are operators of (mass) dimension n, renormalized at a scale m 2 , and C n are the perturbative Wilson coefficients which, in the medium at rest, generally ...

Models based on chiral SU(3) L ⊗ SU(3) R symmetry and vector meson dominance suggest an attractive potential for the ω-meson in a nuclear medium. We discuss the feasibility of producing nuclear bound states of ω-mesons using (d, 3 He) and pion induced reactions on selected nuclear targets.