and ble degeneracy, the mass density of the heavy neutrinos would greatly exceed reasonable cosmological limits.This includes contributions of y, v"v, , v",v",e, e, p, p+; plus three color triplets g, d, s, of quarks and the correspondirg antiquarks; plus eight massless spinone gluons.An upper bound on the lifetime of a massive, neutral, weakly interacting lepton, v~, is derived from standard big-bang cosmology. Saturation of the bound and reasonable assumptions about the weak interaction of the v" then yield a prediction of approximately 10 MeV for its mass.Recently Lee and Weinberg' have pointed out that stable neutrinos with masses in the GeV range are capable of "hiding" a cosmological energy density on the order of p =p, =10 ' MeV/cm'. This density is an order of magnitude greater than proven mass reserves such as galaxies and the cosmic microwave background but is suggested by current best values for the Hubble constant and deceleration parameter. ' It has been shown by Cowsik and McClelland' that stable neutrinos

We give an S-matrix-theoretic demonstration that if the Higgs-boson mass exceeds M, = (8m'/3GF)", parital-wave unitarity is not respected by the tree diagrams for two-body scattering of gauge bosons, and the weak interactions must become strong at high energies. We exhibit the relation of this bound to the structure of the Higgs-Goldstone Lagrangian, and speculate on the consequences of strongly coupled Higgs-Goldstone systems. Prospects for the observation of massive Higgs scalars are noted.

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We analyze the circumstances under which the violations of an approximate symmetry in a unified gauge theory of weak interactions are naturally suppressed; in particular, we investigate approximate muonand electron-type lepton-number conservation as an example of such a symmetry. Extending earlier work, we propose a unified treatment of this symmetry together with strangeness conservation by the weak neutral current and CP invariance. The rate for the decay p,~ey is calculated for a general SU(2))& U(1) gauge model. From this and a similar study of the decay p,~e ee we derive a set of conditions which guarantees that the violation of muonand electron-type lepton-number conservation is naturally strongly suppressed. As part of this, we compute the nondiagonal electromagnetic vertex to one-loop order for an arbitrary SU(2))& U(1) gauge theory. We then focus on the phenomenological predictions of a particular gauge model with three left-handed doublets of leptons and quarks. These include the existence of charged and neutral heavy leptons and of small violations of p,-e universality and the relation GF~sec8c-GP'. Other muonand electron-number-violating effects include nonvanishing rates for the decays K +~n+eP, and KL~eP"and for the reactions p, + N~e + N and v, + N~e + X.

No abstract