Dark Matter in Universe as the Geometry of Empty Space
  The observed excess of gravitational forces in galaxies and galactic clusters is usually referred as the existence of "dark matter particles" of unknown origin. An alternative explanation of the dark matter effect is presented here by assuming that the empty space of the Universe has a complicated geometrical structure. It is assumed that the cosmological Lambda term, which is approximately constant at scales of several Mpc and describes the dark energy, is not constant at scales of several tenth of Kpc and describes the "dark matter effect". This term is mathematically analogous, but not identical, with the energy-momentum tensor of particles ensembles. In this connection the general expression of the Riemann tensor, which depends on the matter distribution in space and on the empty space geometry, is considered. The Ricci tensor does not describe all possible empty space structures. The tensor of the spin curvature also has to be taken into account. Local deviations of the empty space geometry of Universe from a flat one provide the same observational effect as clouds of invisible particles which demonstrate themselves by their gravitational fields only. The matter, which forms stars and galaxies, will concentrate in gravitational depressions of empty space. The gravitation provides correlation of the luminous matter distribution and geometrical structures of space. The presented theory is compared with observations. 
Arkady Z. Dolginov
astro-ph.CO