The Nuclear Force Problem: Is the Never-Ending Story Coming to an End?

The attempts to find the right (underlying) theory for the nuclear force have a long and stimulating history. Already in 1953, Hans Bethe stated that ”more man-hours have been given to this problem than to any other scientific question in the history of mankind”. In search for the nature of the nuclear force, the idea of sub-nuclear particles was created which, eventually, generated the field of particle physics. I will review this productive history of hope, error, and desperation. Finally, I will discuss recent ideas which apply the concept of an effective field theory to low-energy QCD. There are indications that this concept may provide the right framework to properly understand nuclear forces. 1 Historical perspective The theory of nuclear forces has a long history (cf. Table 1). Based upon the seminal idea by Yukawa [1], first field-theoretic attempts to derive the nucleonnucleon (NN) interaction focused on pion-exchange. While the one-pion exchange turned out to be very useful in explaining NN scattering data and the properties of the deuteron [2], multi-pion exchange was beset with serious ambiguities [3, 4]. Thus, the “pion theories” of the 1950s are generally judged as failures—for reasons we understand today: pion dynamics is constrained by chiral symmetry, a crucial point that was unknown in the 1950s. Historically, the experimental discovery of heavy mesons [5] in the early 1960s saved the situation. The one-boson-exchange (OBE) model [6,7] emerged which is still the most economical and quantitative phenomenology for describing the nuclear force [8,9]. The weak point of this model, however, is the scalarisoscalar “sigma” or “epsilon” boson, for which the empirical evidence remains controversial. Since this boson is associated with the correlated (or resonant) exchange of two pions, a vast theoretical effort that occupied more than a decade