Dark Matter or a New Force?

Abstract

We show that a new force, which appeared in a five-dimensional generalization of general relativity, implies precisely the flat circular velocity curves of luminous matter observed in the outer parts of spiral galaxies. A cosmological solution for the new force (not the galactic solution treated in this paper) might explain the cosmic negative, or repulsive, gravitation responsible for the accelerated expansion of the universe, attributed nowadays to ``dark energy'' and sometimes modelled by Einstein's cosmological constant.