Thin disk in higher dimensional space-time and dark matter interpretation

Abstract

We find a family of exact solutions of Einstein equations describing the field of a static axisymmetric thin disk living in six-dimensional space-time. In particular, we study the disks constructed (by cutting out the central part of the space-time) from the conventional Schwarzschild and Chazy-Curzon solutions with simple extensions in the extra 2 dimensions. The disks are interpreted in terms of two counterrotating streams of particles on free circular orbits. Two extra parameters---the constants of motion resulting from projections of the particle-velocities' extra components---are constrained by the requirement that the orbits within the disk be stable. The requirement is met just in cases when the radial profile of the disk orbital speed fits the rotation curves of many spiral galaxies. It thus turns out that the effective modification of the gravity law by extra dimensions could explain the observed flatness of these curves equally well as the usual dark matter interpretation. In the second part of the paper we show that the inclusion of extra dimensions also leads to better fits of the gravitational lensing data for galaxy clusters, without changing results obtained in solar system scales. Finally, we discuss whether the effect of extra dimensions could also be translated as following from the occurrence of extra matter (``Kaluza-Klein particles''). A comment on possible properties of such particles and a chance to detect them at the CERN LHC is given in the Appendix.