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FLAVOR CHANGING TRANSITIONS AND THE TOP QUARK IN A TWO HIGGS DOUBLETS MODEL.pdf

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UCRHEP-T190 May 1997 FLAVOR CHANGING TRANSITIONS AND THE TOP QUARK IN A TWO HIGGS DOUBLETS MODEL; APPLICATION TO e+e? → tc?νeν?e, tc?e+e?, tc?Z, t→ cW+W? AND t→ cZZ 1 S. Bar-Shalom Department of Physics, University of California, Riverside CA 92521. Abstract Extension of the SM with one extra Higgs doublet may give rise to flavor- changing-scalar coupling of a neutral Higgs to a pair of top-charm quarks. This coupling gives rise to a large tree-level effective W+W?;ZZ?Higgs?tc? interaction. We find that the reactions e+e? → tc?νeν?e, tc?e+e?, tc?Z and the two rare top decays t→ cW+W?, t→ cZZ are very sensitive probes of such an effective interaction. The most promising ones, e+e? → tc?νeν?e, tc?e+e?, may yield several hundreds and up to thousands of such events at the Next Linear Collider with a center of mass energy of √ s = 0.5–2 TeV if the mass of the light neutral Higgs is a few hundred GeV. We also find that the rare decays t → cW+W? and t → cZZ may be accessible in the LHC if the mass of the light neutral Higgs lies in the narrow window 150 GeV ~ mh ~ 200 GeV. 1Talk presented at the first FCNC symposium, February 19-21, 1997, Santa Monica, CA USA. Work done in collaboration with G. Eilam, A. Soni and J. Wudka. 1 1 Introductory Remarks The reactions σZtc ≡ σ(e+e? → tc?Z + t?cZ) and in particular σννtc ≡ σ(e+e? → tc?νeν?e + t?cνeν?e) , σeetc ≡ σ(e+e? → tc?e+e?+ t?ce+e?), via W+W? or ZZ fusion, respectively, are extremely sensitive probes for investigations of FC currents at the Next Linear Collider (NLC). Also, in a very narrow window of the Higgs mass detection of the rare top decays t→ cW+W? and t→ cZZ may be possible at the Large Hadron Collider.[1] A two Higgs doublet model with flavor-changing-scalar-transitions (FCST), often called Model III,[2] can give rise to large FCST in top quark systems.[3] In this model there are two neutral scalars, denoted here by h and H, that can couple to vector bosons. Within Model III the above reactions can occur at the tr
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