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##### Medium effects on D properties and N-D transition form factors

**Authors**: C. Christov, M. Fiolhais, E. Ruiz Arriola and K. Goeke

**Ref.**: Physics Letters B **243**, 333-340 (1990)

**Abstract**: The properties of the Delta (1232) isobar immersed in a nuclear medium are investigated in a chiral quark-meson theory. To this end the Nambu-Jona-Lasinio model is used to evaluated the pion decay constant, the pion mass and the sigma mass at finite medium density. These values serve to fix the parameters of the Gell-Mann-Lévi sigma model. The latter is then solved in a variational mean-field and projection approach in order to obtain the static delta properties and gamma N Delta and pi N Delta vertices. At the nuclear matter density both the mass of the delta and the nucleon-delta mass splitting are reduced by about 20%, the radii show swelling and the form factors get noticeably reduced at finite momentum transfers relevant for charge-exchange reactions and electron scattering.