Phenomenology of two Higgs doublet models with flavor-changing neutral currents

Abstract

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.

CP violation in top physics

“…Indeed such couplings with CP-violating phases may also naturally arise in R-parity violating SUSY models [242]. Of course such processes are GIM suppressed in the SM but for the purpose of this discussion we are assuming that there is a FC Higgs sector as in section 3.2.2, thus for the reactions Z * , γ * → tc,tc, rates appreciably larger than the SM may be expected [84,243]. Since many such extensions of the SM contain a large number of unconstrained Yukawa couplings, they will, in general, also contain CP-violating phases.…”

“…We choose not to concern ourselves with the technical aspects of imposing such a U(1) symmetry, but rather concentrate on the CP-violating consequences of a 2HDM with FCNC, the so called Model III. A more detailed discussion about the flavor changing parameters and their experimental constraints can be found, for example, in [84].…”

“…If the Higgs sector contains two or more doublets, then the Higgs couplings may be FC (Flavor Changing) [84,240] (see also section 3.2.2). This can lead to a dramatic tree-level signature of µ + µ − → tc (or ct) due to the neutral Higgs resonance [241].…”

Top flavour-changing neutral coupling signals at a linear collider

“…For instance, in models with exotic quarks Br(t → Zq) can be of order 10 −3 [3]. Two Higgs doublet models allow for Br(t → Zc) = 10 −6 , Br(t → γc) = 10 −7 [4], and in R parity-violating supersymmetric models one can have Br(t → Zc) = 10 −4 , Br(t → γc) = 10 −5 [5]. Top FCN decays into a light Higgs boson and an up or charm quark can also have similar or larger rates in these models [6,4,7].…”

“…Two Higgs doublet models allow for Br(t → Zc) = 10 −6 , Br(t → γc) = 10 −7 [4], and in R parity-violating supersymmetric models one can have Br(t → Zc) = 10 −4 , Br(t → γc) = 10 −5 [5]. Top FCN decays into a light Higgs boson and an up or charm quark can also have similar or larger rates in these models [6,4,7]. Hence, top FCN couplings offer a good place to search for new physics, which may manifest if these vertices are observed in future colliders.…”