A comprehensive phenomenological analysis of a two Higgs doublet model, with flavor-changing scalar currents at the tree-level, called model III, is presented. Constraints from existing experimental information especially on ∆F = 2 processes are systematically incorporated. Constraints emerging from rare B-decays, Z → b b, and the ρ-parameter are also examined. Experimental implications for e + e − (µ + µ − ) → tc + tc, t → cγ(Z, g), D 0 -D0 , and B 0 s -B0 s oscillations, and for e + e − (Z) → bs + bs are investigated and experimental effort towards these is stressed. We also emphasize the importance of clarifying the experimental issues pertaining to Z → b b.

An upgraded analysis of ǫ, x d and ǫ ′ /ǫ, using the latest determinations of the relevant experimental and theoretical parameters, is presented. Using the recent determination of the top quark mass, m t = (174 ± 17) GeV, our best estimate is ǫ ′ /ǫ = 3.1 ± 2.5, which lies in the range given by E731. We describe our determination of ǫ ′ /ǫ and make a comparison with other similar studies. A detailed discussion of the matching of the full theory to the effective Hamiltonian, written in terms of lattice operators, is also given.

In this paper we present a calculation of the ∆S = 1 effective weak Hamiltonian including next-to-leading order QCD and QED corrections. At a scale µ of the order of few GeV, the Wilson coefficients of the operators are given in terms of the renormalization group evolution matrix and of the coefficients computed at a large scale ∼ M W . The expression of the evolution matrix is derived from the two-loop anomalous dimension matrix which governs the mixing of the relevant current-current and penguin operators, renormalized in some given regularization scheme. We have computed the anomalous dimension matrix up to and including order α 2 s and α e α s in two different renormalization schemes, NDR and HV, with consistent results. We give many details on the calculation of the anomalous dimension matrix at two loops, on the determination of the Wilson coefficients at the scale M W and of their evolution from M W to µ. We also discuss the dependence of the Wilson coefficients/operators on the regularization scheme.

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We present a new calculation of the CP violation parameter ǫ ′ /ǫ. The results reported in this paper have been obtained by using the ∆S = 1 effective Hamiltonian computed at the next-to-leading order, including QCD and QED penguins. The matrix elements of the relevant operators have been taken from lattice QCD, at a scale µ = 2 GeV. At this relatively large scale, the perturbative matching between the relevant operators and the corresponding coefficients is quite reliable.The effect of the next-to-leading corrections is to lower the prediction obtained at the leading order, thus favouring the experimental result of E731. We analyze different contributions to the final result and compare the leading and next-to-leading cases.