Abstract : Results are presented from a search for pair production of third-generation scalar and vector leptoquarks, and top squarks, decaying into a tau lepton and a b quark. The search is based on a data sample of pp collisions at sqrt(s) = 7 TeV, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 4.8 inverse femtobarns. The number of observed events containing two tau leptons and two b-tagged jets is found to be in agreement with the standard model prediction. The results are interpreted in several scenarios, with exclusion limits on mass parameters at 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to tau lepton and b quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Limits are also set on the cross section for pair production of top squarks in a supersymmetric model with R-parity violation. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, assuming that the coupling between the top squark, tau lepton, and b quark, lambda'=1; and limits on lambda' are set. These results are the most stringent for these scenarios to date.