Baryon decuplet in the chiral dynamics of Lambda hyperons in nuclear matter

We study the long range part of the Lambda-hyperon optical potential in nuclei using quantum many body techniques and flavor-SU(3) chiral Lagrangians as starting point. More precisely, we study the contributions to the Lambda-hyperon optical potential due to the long-range two-pion exchange, with Sigma and Sigma(*) baryons in the internal baryonic lines and considering Nh and Delta h excitations. We also consider the contribution to the spin-orbit potentials that comes out from these terms. Our results support a natural explanation of the smallness of the Lambda-nuclear spin-orbit interaction and show the importance of the Sigma(*) and Delta degrees of freedom for the hyperon-nucleus interactions