Functional approach to the non-mesonic decay of Lambda-hypernuclei

We present an evaluation of the non-mesonic decay widths for Lambda-hypernu clei (Lambda N-->NN, Lambda NN --> NNN) within the framework of the polariz ation propagator method. The full ii self-energy is evaluated microscopical ly in nuclear matter by using the functional approach, which supplies a the oretically well grounded approximation scheme for the classification of the relevant diagrams, according to the prescriptions of the bosonic loop expa nsion. We employ average Fermi momenta, suitably adapted to different mass number regions (medium-light, medium and heavy hypernuclei). Moreover, we s tudy the dependence of the decay rates on the NN and Lambda N short range c orrelations. With a proper choice of the parameters which control these cor relations in the new approximation scheme, it is possible to reproduce the experimental decay widths for A greater than or similar to 10 hypernuclei. (C) 2000 Elsevier Science B.V. All rights reserved.