Bounds from $t \bar t$ production on R-parity violating models of   supersymmetry
  We study $t \bar t$ production in R-parity violating supersymmetry. The annihilation channel $q \bar q \rightarrow t \bar t$ gets new contributions from $t$-channel exchange of squarks or sleptons. With the data from Tevatron on $t \bar t$ production, we find that the squark- or slepton-exchange processes constrain the $B$-violating $\lambda''$ couplings or the $L$-violating $\lambda'$ couplings, respectively. Our bounds are already comparable to the few existing constraints on third-generation $R$-parity violating couplings, and will improve when more precise measurements of the $t \bar t$ production cross-section become available. We also discuss the effects of these couplings for top production at the LHC. 
Dilip Kumar Ghosh (Bombay U.), Sreerup Raychaudhuri and K. Sridhar   (Tata Inst.)