Role of unitarity in EFT descriptions of low-energy NN scattering

Cut-off regulators in the effective field theory (EFT) description of a low-energy NN scattering often violates unitarity. To understand the phenomenological consequences of such a violation of unitarity, we have performed a comparative study for the 1S0 np scattering up to next-to-leading order with five different forms of regulators, some of which preserve unitarity while others do not. For this aim, we have considered two different types of EFTs; one is the EFT that consists of only nucleonic degrees of freedom, and the other is the EFT with a dibaryon field. For both types of EFTs, unitarity-preserving regulators turn out generally to produce phase shifts in better agreement with the data than unitarity-violating regulators do.