Nuclear forces from chiral Lagrangians using the method of unitary transformation II: The two-nucleon system

We employ the chiral nucleon-nucleon potential derived in ref.[1] to study bound and scattering states in the two-nucleon system. At next-to-leading order, this potential is the sum of renormalized one-pion and two-pion exchange and contact interactions. At next-to-next-to-leading order, we have additional chiral two-pion exchange with low-energy constants determined from pion-nucleon scattering. Alternatively, we consider the Δ(1232) as an explicit degree of freedom in the effective field theory. The nine parameters related to the contact interactions can be determined by a fit to the np S- and P-waves and the mixing parameter ε_1 for laboratory energies below 100 MeV. The predicted phase shifts and mixing parameters for higher energies and higher angular momenta are mostly well described for energies below 300 MeV. The S-waves are described as precisely as in modern phenomenological potentials. We find a good description of the deuteron properties.

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