Search for Rare Charm Meson Decays at FNAL E791

We report the results of a blind search for flavor-changing neutral current (FCNC), lepton-flavor violating, and lepton-number violating decays of D+, Ds+, and D0 mesons (and their antiparticles) into 2-, 3-, and 4-body states including a lepton pair. Such decays may involve Flavor-Changing Neutral Currents, Leptoquarks, Horizontal Gauge Bosons, or Majorana Neutrinos. No evidence for any of these decays is found. Therefore, we present 90% confidence level branching fraction upper limits, typically at the 0.0001 level. A total of 51 decay channels have been examined; 26 have not been previously reported and 18 are significant improvements over previous results.Comment: 15 pages, 5 figures, LaTex, Fermilab E791 Collaboration, References added in revised version, 2nd Frontiers in Contemporary Physics: The Inner Space Outer Space Connection (FCP01), 5-10 Mar 2001, Nashville, Tennessee, US