Vacuum effects of non-nucleonic baryons in nuclear matter

The role of vacuum properties of non-nucleonic baryons in hadronic field theories is discussed. We use an extension of Walecka's σω model treated at the mean-field level. Due to energy considerations the non-nucleonic baryons yield only vacuum effects near normal nuclear matter density. We study the effect of Roper resonance vacuum fluctuations on the nuclear matter equation of state and Coulomb sum. In addition we perform a schematic calculation of the effect of Δ-isobar vacuum fluctuations on the nuclear matter equation of state. Although the Roper resonance produces only a marginal change in the Coulomb sum, the Roper and delta may produce a significant softening of the equation of state. Thus these normally neglected degrees of freedom might serve an important role.