Singlet charge 2\/3 quark hiding the top: Tevatron and LEP implications

If c and t quarks are strongly mixed with a weak singlet charge 2/3 quark, BR(t\to \ell\nu + X) could be suppressed via the t\to cH^0 mode thereby the top quark could still hide below M_W, whereas the heavy quark signal observed at the Tevatron is due to the dominantly singlet quark Q. This may occur without affecting the small m_c value. Demanding m_Q \simeq 175 GeV and m_t \ltap M_W, we find that BR(t\to \ell\nu + X) cannot be too suppressed. The heavy quark Q decays via W,\ H, and Z bosons. The latter can lead to b-tagged Z + 4 jet events, while the strong c--Q mixing is reflected in sizable Q\to sW fraction. Z\to t\bar c decay occurs at tree level and may be at the 10^{-3} order, leading to the signature of Z\to \ell\nu b\bar c, all isolated and with large p_T, at 10^{-5} order.