Elko as an inflaton candidate

Abstract: Elko is a spin-half fermion with a two-fold Wigner degeneracy and Klein-Gordon dynamics. In this paper, we show that in a spatially flat FLRW space-time, slow-roll inflation can be initiated by the homogeneous Elko fields. The inflaton is a composite scalar field obtained by contracting the spinor field with its dual. This is possible because the background evolution as described by the Friedmann equation is completely determined by the scalar field. This approach has the advantage that we do not need to specify the initial conditions for every component of the spinor fields. We derive the equation of motion for the inflaton and also show that this solution is an attractor. Finally, we examine the slow-roll parameters and the power-spectrum, showing that obtaining a behavior in agreement with observational requirements is hard to be obtained, unless one uses more complicated potentials, which may act a limitation of Elko inflation.