Few-nucleon forces and systems in chiral effective field theory

Abstract

We outline the structure of the nuclear force in the framework of chiral effective field theory of QCD and review recent applications to processes involving few nucleons.

Subleading contributions to the three-nucleon contact interaction

“…Nevertheless, despite respresenting only part of the N4LO interaction, the terms derived here could play an important role in the accurate description of the three-nucleon systems, since they are completely unconstrained by symmetries. This is at variance with the 3N N3LO interaction, which contains no free parameters [26,27]. Moreover, the same terms will also appear in the pionless version of the effective theory as next-to-leading 3N interaction and leading 4N interaction.…”

Role of the Total Isospin 3/2 Component in Three-Nucleon Reactions

“…In addition, their magnitude is driven by the strength of the CIB as given by the difference of the corresponding t-matrices √ 2 3 (t t=1 nn − t t=1 np ) in Eq. (6). In such a case, not only the magnitude of CIB decides about the importance of the pqβ|T |φ contributions, but also the isospin T = 3/2 3NF matrix elements, which participate in generating the pqβ|T |φ amplitudes.…”

“…Charge-independence breaking (CIB) is well established in the two-nucleon (2N) system in the 1 S 0 state as evidenced by the values of the scattering lengths −23.75 ± 0.01, −17.3 ± 0.8, and −18.5 ± 0.3 fm [1,2] for the neutron-proton (np), proton-proton (pp) (with the Coulomb force subtracted), and neutron-neutron (nn) systems, respectively. That knowledge of CIB is incorporated into modern, high precision NN potentials, as exemplified by the standard semiphenomenological models: Av18 [3], CD Bonn [4], or NijmI and NijmII [5], as well as by the chiral NN forces [6][7][8]. Treating neutrons and protons as identical particles requires that nuclear systems are described not only in terms of the momentum and spin but also isospin states.…”

Is chiral symmetry manifested in nuclear structure?

“…For nuclear forces, the immediate consequence is the one-pion-exchange (OPE) potential with its long range and characteristic tensor structure. In more detail there are constraints on the form of interactions in effective low-energy Lagrangians [1,2,3]. Since nuclear structure is ultimately determined by low-energy QCD and the nuclear Fermi momentum is comparable to 2m π , one might expect stark evidence from data for the fingerprint of chiral symmetry.…”