Right-handed sneutrino dark matter in $\mathbf{U(1)'}$ seesaw models and
  its signatures at the LHC
  We suggest a real right-handed sneutrino, $\tilde N_1$, as a good dark matter
candidate in a supersymmetric $Z'$ model realizing the seesaw mechanism. When
the extra gaugino, $\tilde Z'$, is lighter than $Z'$, the thermal freeze-out of
the dark matter annihilation to right-handed neutrinos, $ \tilde{N}_1
\tilde{N}_1 \to NN$, through the $t$-channel $\tilde Z'$ exchange is shown to
produce the right dark matter density. It is essential to include the decay and
inverse decay of $N$ in this process, otherwise $N$ decouples too early and
thus dark matter is overproduced. At the LHC, the search for the seesaw
mechanism can be made by observing the signatures of $pp \to \tilde Z' \tilde
Z' \to NN + \ptmiss$ as $\tilde Z'$ can be copiously produced from the cascade
decays of gluinos/squarks, which is complementary to the search of $pp\to Z'
\to NN$. This may also open up a promising new channel of finding the Higgs
boson from the displaced $N$ decay.
