Leading order relativistic chiral nucleon-nucleon interaction
  Motivated by the successes of relativistic theories in studies of atomic/molecular and nuclear systems and the need for a relativistic chiral force in relativistic nuclear structure studies, we explore a new relativistic scheme to construct the nucleon-nucleon interaction in the framework of covariant chiral effective field theory. The chiral interaction is formulated up to leading order with covariant power counting and a Lorentz invariant chiral Lagrangian. We find that the relativistic scheme induces all six spin operators needed to describe the nuclear force. A detailed investigation of the partial wave potentials shows a better description of the $^1S_0$ and $^3P_0$ phase shifts than the leading order Weinberg approach, and similar to that of the next-to-leading order Weinberg approach. For the other partial waves with angular momenta $J\geq 1$, the relativistic results are almost the same as their leading order non-relativistic counterparts. 
Xiu-Lei Ren, Kai-Wen Li, Li-Sheng Geng, Bing-Wei Long, Peter Ring, and   Jie Meng
nucl-th hep-ph