Same-sign trileptons and four-leptons as signatures of new physics at the Large Hadron Collider

We point out that same-sign multilepton events, not given due attention yet for new physics search, can be extremely useful at the Large Hadron Collider. After showing the easy reducibility of the standard model backgrounds, we demonstrate the viability of same-sign trilepton signals for R-parity breaking supersymmetry, at both 7 and 14 TeV. We find that same-sign four-leptons, too, can have appreciable rates. Same-sign trileptons are also expected, for example, in Little Higgs theories with T-parity broken by anomaly terms.