Relativistic treatment of hypernuclear decay

We compute for the first time the decay width of {Lambda}-hypernuclei in a relativistic mean-field approximation to the Walecka model. Due to the small mass difference between the {Lambda}-hyperon and its decay products{emdash}a nucleon and a pion{emdash}the mesonic component of the decay is strongly Pauli blocked in the nuclear medium. Thus, the in-medium decay becomes dominated by the nonmesonic, or two-body, component of the decay. For this mode, the {Lambda}-hyperon decays into a nucleon and a spacelike nuclear excitation. In this work we concentrate exclusively on the pionlike modes. By relying on the analytic structure of the nucleon and pion propagators, we express the nonmesonic component of the decay in terms of the spin-longitudinal response function. This response has been constrained from precise quasielastic ({rvec p},{rvec n}) measurements done at LAMPF. We compute the spin-longitudinal response in a relativistic random-phase-approximation model that reproduces accurately the quasielastic data. By doing so, we obtain hypernuclear decay widths that are considerably smaller{emdash}by factors of 2 or 3{emdash}relative to existing nonrelativistic calculations. {copyright} {ital 1999} {ital The American Physical Society}