  We study the phenomenology of supersymmetric models in which gauge-singlet
scalars mix with the MSSM sneutrinos through weak-scale $A$ terms. After
reviewing the constraints on mixed-sneutrino dark matter from measurements of
$\Omega_{CDM}$ and from direct-detection experiments, we explore
mixed-sneutrino signatures relevant to the LHC. For a mixed-sneutrino LSP and a
right-handed slepton NLSP, decays of the lightest neturalino can produce
opposite-sign, same-flavor (OSSF) dileptons with an invariant-mass distribution
shifted away from the kinematic endpoint. In different parameter regions, the
charginos and neutralinos produced in cascades all decay dominantly to the
lighter sneutrinos, leading to a kinematic edge in the jet-lepton
invariant-mass distribution from the decay chain $\tilde{q} \to \chi^- q \to
\snu^* l q$, without an OSSF dilepton signature. We explore the possibility of
using mass estimation methods to distinguish this mixed-sneutrino jet-lepton
signature from an MSSM one. Finally, we consider signatures associated with
Higgs-lepton or $Z$-lepton production in cascades involving the heavier
sneutrinos.
