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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