2022 Impact factor 4.4
Particles and Fields
Eur. Phys. J. C 10, 51-62
DOI 10.1007/s100529900048

The rare K decays and Z0 penguin contributions in the topcolor-assisted technicolor models

Zhenjun Xiao1,2,3 - Chongsheng Li1,2 - Kuangta Chao1,2

1 CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, P.R. China
2 Department of Physics, Peking University, Beijing 100871, P.R. China
3 Department of Physics, Henan Normal University, Xinxiang 453002, P.R. China

Received: 24 November 1998 / Revised version: 16 February 1999 / Published online: 15 July 1999

We calculate the new contributions to the rare decays K$^+ \to \pi^+
\nu \bar \nu$, ${\mathrm K}_{\mathrm L} \to
\pi^0 \nu \bar \nu$ and ${\mathrm K}_{\mathrm L} \to \mu^+ \mu^-$from new Z0 penguin and box diagrams induced by the unit-charged scalars $(\tilde{\pi}^\pm, \tilde{\mathrm H}^\pm, \pi_1^\pm,
\pi_8^\pm)$appearing in the topcolor-assisted technicolor (TC2) models. We find that: (a) the unit-charged top-pion $\tilde{\pi}^\pm$ and b-pion $\tilde{\mathrm H}^\pm$ can provide large contributions to the rare K decays if they are relatively light; (b) the size of the mixing elements ${\mathrm D}_{\mathrm {L,R}}^{ij}$ ($ i
\neq j $) is strongly constrained by the data of B0 meson mixing: $\vert a_{\mathrm R}^{\mathrm {ts}}\vert, \vert a_{\mathrm R}^{\mathrm {td}}\vert <
0.01$ for $a_{\mathrm L}^{\mathrm {td}}=
a_{\mathrm L}^{\mathrm {ts}}=1/2$ and $m_{\tilde{\mathrm H}^0}\leq
600$GeV; (c) the enhancements to the branching ratios of rare K decays from new scalars can be as large as one order of magnitude; (d) there is a strong cancellation between the short- and the long-distance dispersive part of the decay ${\mathrm K}_{\mathrm L} \to \mu^+ \mu^-$, the constraint on the new short-distance part from this decay mode is thus not strong; (e) the typical TC2 model under study is generally consistent with the available rare K-decay data.

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