Tau flavour violation in sparticle decays at the LHC

We consider sparticle decays that violate τ lepton number, motivated by neutrino oscillation data. We work in the context of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the different sleptons have identical masses at the GUT scale, and neutrino Dirac Yukawa couplings mix them. We find that the branching ratio for decay of the heavier neutralino χ2→χ+τ±μ∓ is enhanced when the LSP mass mχ∼mτ˜1, including the region of CMSSM parameter space where coannihilation keeps the relic χ density within the range preferred by cosmology. Thus χ2→χ+τ±μ∓ decay may provide a physics opportunity for observing the violation of τ lepton number at the LHC that is complementary to τ→μ+γ decay. Likewise, χ2→χ+e±μ∓ decay is also enhanced in the coannihilation region, providing a complement to μ→e+γ decay.