Lepton flavor violation and cosmological constraints on R-parity violation

Abstract

In supersymmetric standard models R-parity violating couplings are severely constrained, since otherwise they would erase the existing baryon asymmetry before the electroweak transition.It is often claimed that this cosmological constraint can be circumvented if the baryon number and one of the lepton flavor numbers are sufficientlyconserved in these R-parity violating couplings, because B/3−Lifor each lepton flavor is separately conserved by the sphaleronprocess.We discuss the effect of lepton flavor violation on the B−L conservation,and show that even tiny slepton mixing angles θ12≳\U0001d4aa(10−4) and θ23,θ13≳\U0001d4aa(10−5) will spoil the separate B/3−Li conservation. In particular, if lepton flavor violations are observed in experiments such as MEG and B-factories, it will imply that all the R-parity violating couplings must be suppressedto avoid the B−L erasure. We also discuss the implication for the decay of the lightest MSSM particle at the LHC.