Dark Matter-Motivated Searches for Exotic 4th Generation Quarks in
  Tevatron and Early LHC Data
  We determine the prospects for finding dark matter at the Tevatron and LHC
through the production of exotic 4th generation quarks T' that decay through T'
\to t X, where X is dark matter. The resulting signal of t \bar{t} + \met has
not previously been considered in searches for 4th generation quarks, but there
are both general and specific dark matter motivations for this signal, and with
slight modifications, this analysis applies to any scenario where invisible
particles are produced in association with top quarks. Current direct and
indirect bounds on such exotic quarks restrict their masses to be between 300
and 600 GeV, and the dark matter's mass may be anywhere below m_T'. We simulate
the signal and main backgrounds with MadGraph/MadEvent-Pythia-PGS4. For the
Tevatron, we find that an integrated luminosity of 20 fb^-1 will allow 3\sigma
discovery up to m_T' = 400 GeV and 95% exclusion up to m_T' = 455 GeV. For the
10 TeV LHC with 300 pb^-1, the discovery and exclusion sensitivities rise to
490 GeV and 600 GeV. These scenarios are therefore among the most promising for
dark matter at colliders. Perhaps most interestingly, we find that dark matter
models that can explain results from the DAMA, CDMS and CoGeNT Collaborations
can be tested with high statistical significance using data already collected
at the Tevatron and have extraordinarily promising implications for early runs
of the LHC.
