Nuclear Forces and Nuclear Structure

After a historical review, I present the progress in the field of realistic NN potentials that we have seen in recent years. A new generation of very quantitative (high-quality/high-precision) NN potentials has emerged. These potentials will serve as reliable input for microscopic nuclear structure calculations and will allow for a systematic investigation of off-shell effects. The issue of three-nucleon forces is also discussed.Comment: Invited Talk presented at Nuclear Structure '98, Gatlinburg, Tennessee, August 10-15, 1998; 15 pages, 6 figures, aipproc2.sty and epsfig.st

Recent Advances in the Theory of Nuclear Forces and its Impact on Microscopic Nuclear Structure

The theory of nuclear forces has made great progress since the turn of the millenium using the framework of chiral effective field theory (ChEFT). The advantage of this approach, which was originally proposed by Weinberg, is that it has a firm basis in quantum-chromodynamics and allows for quantitative calculations. Moreover, this theory generates two-nucleon forces (2NF) and many-body forces on an equal footing and provides an explanation for the empirically known fact that 2NF >> 3NF >> 4NF. I will present the recent advances in more detail and put them into historical context. In addition, I will also provide a critical evaluation of the progress made including a discussion of the limitations of the ChEFT approach.Comment: 8 pages, 2 figures, talk at EXOCT 2007, Catania, Italy, June 11-15, 200

From Quarks to Nuclei: Challenges of Lattice QCD

I discuss challenge of lattice QCD, from quarks to nuclei, which connects QCD with nuclear physics.Comment: 7 pages, 10 figures, A talk given in the panel discussion "Fundamental challenge of QCD", at 47. Internationale Universit\"atswochen f\"ur Theoretical Physik Schladming, Stria, Austria, 28 February - 7 March, 200

Off-Shell NN Potential and Triton Binding Energy

The NONLOCAL Bonn-B potential predicts 8.0 MeV binding energy for the triton (in a charge-dependent 34-channel Faddeev calculation) which is about 0.4 MeV more than the predictions by LOCAL NN potentials. We pin down origin and size of the nonlocality in the Bonn potential, in analytic and numeric form. The nonlocality is due to the use of the correct off-shell Feynman amplitude of one-boson-exchange avoiding the commonly used on-shell approximations which yield the local potentials. We also illustrate how this off-shell behavior leads to more binding energy. We emphasize that the increased binding energy is not due to on-shell differences (differences in the fit of the NN data or phase shifts). In particular, the Bonn-B potential reproduces accurately the $\epsilon_1$ mixing parameter up to 350 MeV as determined in the recent Nijmegen multi-energy NN phase-shift analysis. Adding the relativistic effect from the relativistic nucleon propagators in the Faddeev equations, brings the Bonn-B result up to 8.2 MeV triton binding. This leaves a difference of only 0.3 MeV to experiment, which may possibly be explained by refinements in the treatment of relativity and the inclusion of other nonlocalities (e.~g., quark-gluon exchange at short range). Thus, it is conceivable that a realistic NN potential which describes the NN data up to 300 MeV correctly may explain the triton binding energy without recourse to 3-N forces; relativity would play a major role for this result.Comment: 5 pages LaTeX and 2 figures (hardcopies, available upon reqest), UI-NTH-940

Triton Binding Energy and Minimal Relativity

For relativistic three-body calculations, essentially two different approaches are in use: field theory and relativistic direct interactions. Results for relativistic corrections of the triton binding energy obtained from the two approaches differ even in their sign, which is rather puzzling. In this paper, we discuss the origin of such discrepancy. We show that the use of an invariant two-body amplitude, as done in the field-theoretic approach, increases the triton binding energy by about 0.30 MeV. This may explain a large part of the discrepancy.Comment: 11 pages, LaTeX, no figure

How sensitive are various NN observables to changes in the πNN\pi NN coupling constant?

The deuteron, NN analyzing powers A_y, and the singlet scattering length show great sensitivity to the $\pi NN$ coupling constant $g_\pi$. While the pp A_y data favor $g^2_\pi/4\pi\leq 13.6$, the np A_y data and the deuteron quadrupole moment imply $g^2_\pi/4\pi\geq 14.0$. The two diverging values could be reconciled by the assumption of (substantial) charge-splitting of $g_\pi$. However, the established theoretical explanation of the charge-dependence of the $^1S_0$ scattering length (based upon pion mass splitting) is very sensitive to a difference between $g_{\pi^0}$ and $g_{\pi^\pm}$ and rules out any substantial charge-splitting of $g_\pi$. Thus, there are real and large discrepancies between the values for $g_\pi$ extracted from different NN observables. Future work that could resolve the problems is suggested.Comment: Latex, 19 pages, 4 figures; invited talk presented at the Workshop on `Critical Points in the Determination of the Pion-Nucleon Coupling Constant', Uppsala (Sweden), June 7-8, 199