Abstract
During the past few decades a large effort has been made towards describing the NN interaction in the framework of chiral Effective Field Theory (EFT). The main idea is to exploit the symmetries of QCD to obtain an effective theory for low energy nuclear systems. In 2003, the first accurate charge-dependent $NN$ potential in this scheme was developed and it has been applied to many ab-initio calculations, opening the possibility to study nuclear systems in a systematic and accurate way. It was shown that the fourth order (N3LO) was necessary and sufficient to describe the NN scattering data with a $\chi^2/$d.o.f of the order of one. However the systematics of chiral EFT also allow to relate two- and many-body interactions in a well-defined way. Since many-body forces make their first appearance at higher order, they are substantially smaller then their two-body counterparts, but may never-the-less be crucial for some processes. Thus, there are observables where they can have a big impact and they are expected to solve problems like the long standing Ay puzzle of N-d scattering. The last few years, have also seen substantial progress towards higher orders of chiral EFT which was motivated by the fact that only three-body forces of rather high order may solve some outstanding issues in microscopic nuclear structure and reactions. In this chapter we will review the chiral EFT based potentials that have been developed up to N4LO as well as first calculations conducted for NN scattering at N5LO.
Highlights
The modern view of the NN interaction is given in the framework of Chiral Effective Field Theory
Np phase shifts are displayed in Figure 15, which reflect the same features as the χ2, namely, an excellent convergence when going from NNLO to N3LO and, to N4LO
Is equivalent to an effective field theory which allows for a perturbative expansion that has become known as chiral perturbation theory
Summary
The modern view of the NN interaction is given in the framework of Chiral Effective Field Theory (χEFT). The traditional renormalization condition used to build theories like QCD is not required and a renormalization order by order is used instead. Nowadays, this approach is widely applied in different areas of physics. Applying the EFT concept to nuclear systems allows to build theories for nucleons and pions that are consistent with the symmetries of the underlying theory. In the case of QCD, a very important property for low energy dynamics is that the original approximate chiral symmetry is broken spontaneously. This effect makes the pion come into play
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