The Missing Three-Nucleon Forces: Where Are They?

Understand

In recent years, there has been substantial progress in the derivation of nuclear forces from chiral effective field theory.

• Accurate two-nucleon forces (2NF) have been constructed up to next-to-next-to-next-to-leading order (N3LO) of chiral perturbation theory and applied in microscopic nuclear structure calculations with a good degree of success.
• However, chiral three-nucleon forces (3NF) have been used only at N2LO, improving some miscroscopic predictions, but leaving also several issues, like the "Ay puzzle'" of nucleon-deuteron scattering, unresolved.
• Thus, the 3NF at N3LO is needed for essentially two reasons: For consistency with the 2NF, and to (hopefully) improve some critical predictions of nuclear structure and reactions.