Exact solutions to Elko spinors in spatially flat   Friedmann-Robertson-Walker spacetimes
  In this paper we present exact solutions to the so-called Elko spinors for three models of expanding universe, namely the de Sitter, linear and the radiation type evolution. The study was restrict to flat, homogeneous and isotropic Friedmann-Robertson-Walker backgrounds. Starting with an Elko spinor we present the solutions for these cases and compared to the case of Dirac spinors. Besides, an attempt to use Elko spinors as a dark energy candidate in the cosmological context is investigated. 
J. M. Hoff da Silva and S. H. Pereira
hep-th