Towards a relativity of dark-matter rods and clocks
  In the absence of dark matter, the dynamical and kinematical interpretations
of the special relativistic spacetime have been and still are the topic of
philosophic debate, which whilst fertile, is by and large of little predictive
power. This changes dramatically if the debate includes a dark matter candidate
in a "non-trivial" extension of the standard model. Here I argue that rods and
clocks made out of dark matter may not reveal the same underlying algebraic
structure as the rods and clocks made out of standard model particles. For the
sake of concreteness I here exemplify the argument by looking at a particular
dark matter candidate called Elko. Inevitably, one is led to the conclusion
that gravity within the dark sector, and at the interface between dark matter
and standard-model matter, may deviate from the canonical general relativistic
predictions. For Elko dark matter such effects will be of second order in the
sense that they will depend only on the angular momentum and spin of the
gravitational environment.
