  A detailed study of a fermionic quintuplet dark matter in a left-right
symmetric scenario is performed in this article. The minimal quintuplet dark
matter model is highly constrained from the WMAP dark matter relic density (RD)
data. To elevate this constraint, an extra singlet scalar is introduced. It
introduces a host of new annihilation and co-annihilation channels for the dark
matter, allowing even sub-TeV masses. The phenomenology of this singlet scalar
is studied in detail in the context of the Large Hadron Collider (LHC)
experiment. The production and decay of this singlet scalar at the LHC give
rise to interesting resonant di-Higgs or diphoton final states. We also
constrain the RD allowed parameter space of this model in light of the ATLAS
bounds on the resonant di-Higgs and diphoton cross-sections.
