A minimal extension of the standard model is proposed to incorporate the light-neutrino masses and the resolution of the strong CP problem. A unique light pseudo-Goldstone boson, whose coupling to the electron is 1 or 2 orders of magnitude greater than that of the conventional hadronic axion, arises from the model. The scale of Peccei-Quinn symmetry breaking is shown to be greater than 10 10 GeV through its connection to the light-neutrino masses, and is further constrained if the (hypothetical) fourth family of quarks and leptons exists.
The existence of the fourth family heavy unstable neutrino v4 with my4 > m~ and the dominant mixing angle J Ux4Jz=0.042-0.10, is postulated from the present data on the lifetime and the leptonic branching ratios of the x-. The fast decay of a heavy v4 makes it undetectable in present experiments, while the future detection at Z ° factories is shown to be very promising, provided my4 ~< 46 GeV. The contributions of this massive v4 and other fourth family fermions to the total decay widths ofZ ° and W-+ are considered. If the 90% CL of the present UA2's data on Fz/Fw is valid, either the t-quark or v4 or both should be seen (mr ~< 76 GeV or mv, ~<46 GeV) in the near future. Neutrino counting via e+e-~yv9 is predicted to yield N~=3. The mass of the fourth family charged lepton is predicted to be mL ~< 43 GeV if the prototype relation between the mixing angle and the mass eigenvalues is valid. The present UAI's bound on mL, mL~>41 GeV, is shown to be invalid, while the correct lower bound is the 25 GeV of TRISTAN, implying the likely possibility of detecting the fourth charged lepton L +-in the present and forthcoming e+e-colliders. These predictions can be tested in the near future at the Z ° factories at SLC and LEP.
We propose that the observed Ba°-Ba-° mixing reported by ARGUS and CLEO is due to the tree-level flavor changing neutral coupling of the standard model Higgs scalar, H °, or the Z °, induced by new physics with a mass scale beyond the standard model. The strengths of the flavor changing couplings of H ° and Z ° are shown to be increasing with the masses of the fermion flavors involved. If the observed B°-l] ° mixing is due to the flavor changing coupling of H °, the key predictions are D°-D ° mixing of O(10%) of the present experimental upper limit and BR(la--~e-y) ~ ( 1.1 _+0.6)X 10 ~z, and the mass of the Higgs scalar M, ~_ (200-300) GeV, In case the observed Bd°-Ba-° mixing is due to the flavor changing coupling of Z °, the rare decay mode la--~e e+e is predicted to be observable at any time in the near future with the branching ratio in the neighborhood of the present experimental upper limit, while other predictions include: D°-I) ° mixing of O( 1-10)% of the present upper limit, BR( B~t +~t-X ) -~ (8.5 _+ 4.2) X 10 -s, BR(z ~t-~+bt -) -~ (8.8 _+ 4.8 ) X 10 s, and the branching ratios for the flavor changing decay modes ofZ °, BR(Z°-bs+sl3)x 107-~ (14_+ 7), BR(Z°~tc+ct)X 107-~ (1500_+700)(mJ60 GeV), BR(Z°-~b'l~+bl3 ' ) X I07~ (4800±2300) (rob /50 GeV), BR(Z°~kt-z+ +p+z ) X 107~3.6-+ 1.8, and BR(Z°-~'~ ' ~+~"~) X 107~ (1300_+600) (m~/ 40 GeV). These flavor changing branching ratios of Z ° can be tested at LEP with 107 Z°'s. From the observed strength of B~-B ° mixing the scale of new physics can be inferred to be M-~ 250 GeV.
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