The hypertriton in effective field theory

Doublet Lambdad scattering and the hypertriton are studied in the framework of an effective field theory for large scattering lengths. As in the triton case, consistent renormalization requires a one-parameter three-body force at leading order whose renormalization group evolution is governed by a limit cycle. Constraining unknown parameters from symmetry considerations and the measured binding energy of the hypertriton, we calculate the low-energy phase shifts for doublet Ad scattering. For the low-energy parameters, we find a(Lambdad) = (16.8(-2.4)(+4.4)) fm and r(Lambdad) = (2.3 +/- 0.3) fm, where the errors are due to the uncertainty in the hypertriton binding energy. Since the hypertriton is extremely shallow, low-energy three-body observables in this channel are very insensitive to the exact values of the LambdaN low-energy parameters. (C) 2002 Elsevier Science B.V. All rights reserved.