Theoretical Perspectives on Strange Physics

Kaons are heavy enough to have an interesting range of decay modes available to them, and light enough to be produced in sufficient numbers to explore rare modes with satisfying statistics. Kaons and their decays have provided at least two major breakthroughs in our knowledge of fundamental physics. They have revealed to us CP violation,l and their lack of flavor-changing neutral interactions warned us to expect charm.:! In addition, K” K” mixing has provided us with one of our most elegant and sensitive laboratories for testing quantum mechanics.3 There is every reason to expect that future generations of kaon experiments with intense sources would add further to our knowledge of fundamental physics. This talk attempts to set f.uture kaon experiments in a general theoretical context, and indicate how they may bear upon fundamental theoretical issues. Figure 1 encapsulates some important trends in elementary particle physics. Two major philosophical approaches can be distinguished. The “onion-skin” philosophy emphasizes the search for more elementary constituents of matter as previous levels are shown to be composite. Many authors believe4 that the present “elementary” particles such as quarks, leptons, possibly gauge bosons and maybe Higgs fields are in fact composites of underlying preons on a distance scale 5 0(10-16) cm. The unification merchants, on the other hand, emphasize5 the common origin and form of the different fundamental forces. It now seems established that the weak and electromagnetic interactions are at least partially unified in the Glashow-Salam-Weinberg (GSW) model,6 and that the nuclear forces are complicated manifestations of an underlying gauge theory &CD’ which is conceptually close to the GSW model. Together they constitute the “Standard Model” of elementary particles. Their family resemblance leads naturally to the hypothesis’ of a grand unified theory of all gauge interactions. If this exists, its grand symmetry must be broken at a very high energy scale’ within a few orders of magnitude of the Planck mass of O(lOlg) GeV. At that scale there may be a final “superunification” with gravity. The provocative prefix “super” reflects my belief that such a final unification probably employs supersymmetry (SUSY) in some f0rm.l’ It may well be that SUSY makes an earlier appearance on the stage of unification. As we will see later, technical difficulties with GUTS would be alleviated if SUSY was effectively restored at an energy scale as low as 1 TeV.