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Macroscopic Theory of Dark Sector

DOI: 10.1155/2014/586958

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A simple Lagrangian with squared covariant divergence of a vector field as a kinetic term turned out to be an adequate tool for macroscopic description of the dark sector. The zero-mass field acts as the dark energy. Its energy-momentum tensor is a simple additive to the cosmological constant. Massive fields describe two different forms of dark matter. The space-like massive vector field is attractive. It is responsible for the observed plateau in galaxy rotation curves. The time-like massive field displays repulsive elasticity. In balance with dark energy and ordinary matter it provides a four-parametric diversity of regular solutions of the Einstein equations describing different possible cosmological and oscillating nonsingular scenarios of evolution of the Universe. In particular, the singular big bang turns into a regular inflation-like transition from contraction to expansion with the accelerated expansion at late times. The fine-tuned Friedman-Robertson-Walker singular solution is a particular limiting case at the lower boundary of existence of regular oscillating solutions in the absence of vector fields. The simplicity of the general covariant expression for the energy-momentum tensor allows displaying the main properties of the dark sector analytically. Although the physical nature of dark sector is still unknown, the macroscopic theory can help analyze the role of dark matter in astrophysical phenomena without resorting to artificial model assumptions. 1. Introduction Currently there are two most intriguing long standing problems in astrophysics pointing to the existence of so called “hidden sector,” containing “dark energy” and “dark matter.” So far their interaction with the ordinary matter (baryons and leptons) is observed only via gravitation. The first problem, named “galaxy rotation curves,” appeared in 1924, after Oort discovered the galactic halo, a group of stars orbiting the Milky Way outside the main disk [1]. In 1933, Zwicky [2] postulated “missing mass” to account for the orbital velocities of galaxies in clusters. The second problem is the accelerated expansion of the Universe discovered through observations of distant supernovae by Riess and Perlmutter and their colleagues in 1998 [3, 4]. At first glance, these two problems have little to do with one another. The accelerated expansion of the Universe indicates the existence of a hidden mechanism of repulsion [5], while the plateau of the galaxy rotation curves is the result of additional attraction caused by the dark matter [6]. Macroscopic approach to the dark sector problems,

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