NUCLEON-NUCLEON AND HYPERON-NUCLEON EFFECTIVE INTERACTIONS

Nuclear structure calculations are usually performed in a small trunca ted model space, and an essential input to such calculations is the mo del-space effective interaction V(eff). We review here some recent dev elopments concerning microscopic derivations of such effective interac tions, starting from the free nucleon-nucleon(NN) and hyperon-nucleon( YN) interactions. A first step is to calculate the model-space NN and YN G matrix, which can now be performed accurately. One then calculate s the irreducible vertex function Q-box using the G matrix. V(eff) is given by a Q-box folded-diagram series, which, for a given Q-box, can be summed up to all orders using either the Lee-Suzuki or the Krencigl owa-Kuo iteration methods. We discuss also several realistic models fo r the free NN and YN interactions, and a new method of Suzuki and Okam oto for deriving Hermitian effective interactions.