Effects of short-range correlations on Λ decay in nuclear matter

The effects of short-range correlations on the single-particle (sp) properties of a lambda hyperon in nuclear matter are investigated within the Green's function formalism. The calculated spectral function and quasi-particle parameters are qualitatively similar to those which have been observed for nucleons. The lambda spectral function, calculated for a realistic hyperon-nucleon interaction, indicates that about 15% of the sp strength is removed from the quasi-particle region to higher energy as a result of coupling to two-particle-one-hole states. This is compared to about 30% for a nucleon at the Fermi momentum in a similar calculation. A strong coupling between ΛN and ΣN states is known to be crucial for a correct determination of the lambda sp spectrum and gives rise to threshold effects in the self-energy and spectral function. It is also found to have a previously overlooked impact on the weak decay width. The primary decay mode for the lambda hyperon in a dense nuclear medium is a non-mesonic Λ N → NN decay. A consistent treatment of short-range correlations in the ΛN state, going beyond the customary use of a simple multiplicative correlation function, leads to a substantial increase in the decay width. In particular, it is observed that the Σ N → NN decay channel rises to prominence on the strength of the tensor coupling between ΛN and Σ N states. As a result, the contribution to the decay width from the strong conversion to the ΣN state prior to subsequent weak decay of the Σ increases the decay width by a factor of 2. This enhancement of the pion mediated ΛN → Σ N → NN decay channel also limits the impact which a consideration of strange meson exchange can have on the important Γ _n/Γ_p ratio.