QCD sum rules at finite density in the large-image limit: the coupling of the ρ-nucleon system to the image Original Research Article

QCD sum rules are studied for the vector–isovector current at finite baryon density in the limit of large number of colors Nc. For the condensate side it is shown that in this limit the four-quark condensate factorizes also for the finite density case. At the hadronic side the medium dependence is expressed in terms of the current–nucleon forward scattering amplitude. Generalizing vector meson dominance we allow for a direct coupling of the current to the nucleon as well as a coupling via the ρ meson. We discuss the Nc dependence of (a) modifications of the pion cloud of the ρ meson, (b) mixing with other mesons (in particular a1 and ω) and (c) resonance-hole excitations View the MathML source. We show that only the last effect survives in the large-Nc limit. Saturating the sum rules with a simple hadronic ansatz which allows for the excitation of the D13(1520) we determine the coupling of the latter to the ρ-nucleon and the photon–nucleon system. These couplings are hard to determine from vacuum physics alone.