Search for rare top-quark decays at the LHC

Flavour-changing neutral-current (FCNC) top quark decays are suppressed by the GIM mechanism, but are enhanced by BSM models. Any evidence for top-quark FCNC decays could be an evidence for new physics. Searches for the FCNC decays $t\to qX$ where $X=Z,\gamma,H,g$ and $q=u,c$ performed by the ATLAS and CMS Collaborations are presented. Data collected during 2011 and 2012 from proton-proton ($pp$) collisions at the LHC at a centre-of-mass energy of $\sqrt{s}=7$ and 8 TeV, corresponding to integrated luminosities ranging from 2.1 fb$^{-1}$ to 25 fb$^{-1}$, are analysed. Top-quark pair-production events with one top quark decaying through the $t\to qZ,q\gamma,qH$ channels and the other through the dominant Standard Model mode $t\to bW$ are considered as signal, as well as direct top production for the $t\to qg$ channel. No evidence for FCNC signals are found and upper limits on the $t\to qX$ branching ratios are set at 95\% confidence level.