Einstein's basement - A model of dark matter and dark energy?

The energy-momentum relationship (EMR) of a free particle in special relativity is regarded as the upper branch of an avoided crossing between the mass of the particle and its momentum. The corresponding EMR for the lower branch - a regime dubbed as Einstein's basement - is derived. From the associated Lagrangian and the conventional gravitational interaction a new kinematics in Einstein's basement is determined. It is shown that this can lead to a repulsion of the basement particles and a modified interaction with regular matter. The model suggests the identification of the basement particles with dark matter accompanied with a missing interaction with light. The expansion of the basement particles and the regular mass that is carried along could be interpreted as an expansion of the universe. Tests of the model by astronomical observations are suggested.