Limits on muon-neutrino to tau-neutrino oscillations induced by a sterile neutrino state obtained by OPERA at the CNGS beam

The OPERA experiment, exposed to the CERN to Gran Sasso $ u_mu$ beam, collected data from 2008 to 2012. Four oscillated $ u_tau$ Charged Current interaction candidates have been detected in appearance mode, which are consistent with $ u_mu to u_tau$ oscillations at the atmospheric $Delta m^2$ within the standard three-neutrino framework. In this paper, the OPERA $ u_tau$ appearance results are used to derive limits on the mixing parameters of a massive sterile neutrino.