The fifth force

The gaugeless limit helps to clarify and expose the heart of the problems confronting the standard-model. The existence of a residual force not proportional to gauge couplings manifests itself very clearly, and it is difficult to avoid facing its reality. Whether this is a fifth force is an arguable matter of semantics. If the weak force is what is mediated by W and Z, then the 5th force may be as yet undiscovered. However, we must still conclude that the W-exchange force is not ''pure gauge'', it is nonvanishing in the gaugeless limit. What is to be done if the phenomenological formulae for the W masses and for the partial width into electron and its neutrino are renounced. That is all that is needed to infer electron instability in the gaugeless limit. This is not to say that there are no alternatives possible, only that alternatives require a serious change or extension of the conventional point of view. What might such alternatives be. Perhaps in some extended theory (e.g. GUT) the gauge couplings are themselves functions of some parameter, call it λ, which has the property that α → 0 as λ → 0. It may be that some of the remaining standard-model parameters (e.g. quark and lepton masses) also vanish as λ → 0; this would then protect electron stability. This state of affairs might occur because the Yukawa couplings of fermions to the Nambu-Goldstone bosons W vector vanish as λ → 0 or even that GF → ∞ as λ → 0. And if superstring theory fulfills the promises of its prophets, then it may be arguable that the α's are not parameters at all and cannot be varied, since the theory contains no free dimensionless parameters