UC Irvine

We propose that the observed Bd0-B̄d0 mixing reported by ARGUS and CLEO is due to the tree-level flavor changing neutral coupling of the standard model Higgs scalar, H0, or the Z0, induced by new physics with a mass scale beyond the standard model. The strengths of the flavor changing couplings of H0 and Z0 are shon to be increasing with the masses of the fermion flavors involved. If the observed Bd0-B̄d0 mixing is due to the flavor changing coupling of H0, the key predictions are D D0-D̄0 mixing of O (10%) of the present experimental upper limit and BR(μ-å e-γ) ≅ (1.1 ± 0.6) × 10-12, and the mass of the Higgsscalar MH≅(200-300) GeV. In case the observed Bd0 - B̄d0 mixing is due to the flavor changing coupling of Z0, the rare decay mode μ-åe-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: D0-D̄0 mixing of O(1-10)% of the present upper limit, BR(Bs0å μ+μ-X) ≅ (8.5 ± 4.2) × 10-5, BR(τt-å μ-μ+μ-) ≅ (8.8 ±4.8) × and the branching ratios for the flavor changing decay modes of Z0, BR(Z0åbs̄ + ss̄) × 107 ≅ (14 ±7), BR (Z0å tc̄ + ct̄) × 107 ± (1500 ± 700)(mt/60 GeV), BR(Z0å b′b̄ +bb̄′) × 107 ≅ (4800 ± 2300)(mb/50 GeV), BR (Z0å μ-τ+ + μ+τ-) × 3.6 ± 1.8, and BR (Z0å τ′ τ̄ + τ̄′τ) × 107 ≅ (1300 ± 600) (mτ/40 GeV). These flavor changing branching ratios of Z0 can be tested at LEP with 107 Z0′s. From the observed strength of Bd0-B̄d0 mixing the scale of new physics can be inferred to be M ≅ 250 GeV. © 1989.