Cosmological Kinetic Mixing
  In this paper we generalize the kinetic mixing idea to time reparametrization
invariant theories, namely, relativistic point particles and cosmology in order
to obtain new insights for dark matter and energy. In the first example, two
relativistic particles interact through an appropriately chosen coupling term.
It is shown that the system can be diagonalized by means of a non-local field
redefinition, and, as a result of this procedure, the mass of one the particles
gets rescaled. In the second case, inspired by the previous example, two
cosmological models (each with its own scale factor) are made to interact in a
similar fashion. The equations of motion are solved numerically in different
scenarios (dust, radiation or a cosmological constant coupled to each sector of
the system). When a cosmological constant term is present, kinetic mixing
rescales it to a lower value which may be more amenable to observations.
