Flavor changing neutral currents in ttbar decays at D\O

We present a search for flavor changing neutral currents (FCNC) in decays of top quarks. The analysis is based on a search for $t\bar{t}\to {\mathrm{\ell }}^{\mathrm{\prime }}\nu \mathrm{\ell }\bar{\mathrm{\ell }}$+jets ($\mathrm{\ell },{\mathrm{\ell }}^{\mathrm{\prime }}=e,\mu$) final states using 4.1 {\rm fb}${}^{-1}$ of integrated luminosity of $p\bar{p}$ collisions at $\sqrt{s}=1.96$ {\rm TeV}. We extract limits on the branching ratio $B(t\to Zq)$ ($q=u,c$ quarks), assuming anomalous $tuZ$ or $tcZ$ couplings. We do not observe any sign of such anomalous coupling and set a limit of $B<3.2$ at 95% C.L.