Effective field theory with dibaryon degrees of freedom

Abstract

We propose a low energy effective field theory of QCD at the scale of pion mass for the ${N}_{B}=2$ sector, ${N}_{B}$ being the baryon number, which contains two dibaryon fields in addition to the nucleons and pions. It has a well-defined counting is renormalizable, and the nucleon-nucleon scattering amplitudes are manifestly unitary at leading order. We work out a lower energy effective theory for nucleons with energy much lower than the pion mass and three-momentum comparable to it, which also has a well-defined counting and is renormalizable. The dibaryon fields must also be kept as explicit degrees of freedom in this theory. We calculate the scattering amplitudes at next-to-leading order for the ${}^{1}{S}_{0}$ and ${}^{3}{S}_{1}$ channels in this framework and obtain an excellent description of the phase shifts for center-of-mass energies in the 0--50 MeV range.