Here we report that Elko (for Eigenspinoren des Ladungskonjugationsoperators) breaks Lorentz symmetry in a rather subtle and unexpected way by containing a “hidden” preferred direction. Along this preferred direction, a quantum field based on Elko enjoys locality. In the form reported here, Elko offers a mass dimension one fermionic dark matter with a quartic self-interaction and a preferred axis of locality. The locality result crucially depends on a judicious choice of phases.

• Received 6 October 2009

DOI:https://doi.org/10.1103/PhysRevD.83.065017