Λ N N and Σ N N systems at threshold

We calculate the hypertriton binding energy and the Lambda d and Sigma d scattering lengths using baryon-baryon interactions obtained from a chiral constituent quark model. We study consistently the Lambda NN and Sigma NN systems by analyzing the effect of the Sigma <->Lambda conversion. Our interactions correctly predict the hypertriton binding energy. The (I,J)=(0,3/2) Lambda NN channel is also attractive and it might have a bound state. From the condition of nonexistence of a (0,3/2) Lambda NN bound state, an upper limit for the spin-triplet Lambda N scattering length is obtained. We also present results for the elastic and inelastic Sigma N and Lambda N cross sections. The consistent description of the Sigma N scattering cross sections imposes a lower limit for the corresponding spin-triplet scattering lengths. In the Sigma NN system the only attractive channels are (I,J)=(1,1/2) and (0,1/2), the (1,1/2) state being the most attractive one.