# Theory Center Research Highlights

### Few-Body Nuclear Physics and the Nucleon-Nucleon Force

**
"Covariant spectator theory of np scattering: Phase shifts and
covariant one-boson-exchange potentials obtained from high precision fits
to data below 350 MeV"
**

F. Gross and A. Stadler

*Phys. Lett. B*

**657**, 176 (2007) &

*arXiv:0802.1552 [nucl-th]*

A major goal of nuclear physics and the JLab scientific program is to
obtain an understanding of the nuclear force. Part of this effort
involves finding a potential that will give a high precision fit to the
*NN* data below 350 MeV. The well known Nijmegen, Argonne, and Bonn
(Idaho) potentials are to some extent based on one boson exchange (OBE),
but in order to achieve an essentially perfect fit to the scattering data
they all had to abandon OBE and lose the easy extension to electromagnetic
processes provided by this simple mechanism. Recently, using the covariant
spectator theory, a covariant OBE potential has been found that gives an
excellent high precision fit to the *NN* scattering data (see the
table). Furthermore, this potential has fewer adjustable parameters than
previous high-precision potentials, and also reproduces the experimental
triton binding energy without additional irreducible three-nucleon forces.
This simple new force is now being used to study few-body measurements at
JLab.

**
"Few-nucleon forces and systems in chiral effective field theory"
**

E. Epelbaum

*Prog. Part. Nucl. Phys.* **57**, 654 (2006)

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.

**
"Modern theories of low-energy astrophysical reactions"
**

L.E. Marcucci, K.M. Nollett, R. Schiavilla, R.B. Wiringa

*Nucl. Phys.* **A777**, 111 (2006)

We summarize recent ab initio studies of low-energy electroweak
reactions of astrophysical interest, relevant for both big bang
nucleosynthesis and solar neutrino production. The calculational methods
include direct integration for *np* radiative and *pp* weak
capture, correlated hyperspherical harmonics for reactions of *A*=3,4
nuclei, and variational Monte Carlo for *A*=6,7 nuclei. Realistic
nucleon-nucleon and three-nucleon interactions and consistent current
operators are used as input.