Graviton, ghost and instanton condensation on horizon scale of the   Universe. Dark energy as a macroscopic effect of quantum gravity
  We show that cosmological acceleration, Dark Energy (DE) effect is a consequence of the zero rest mass, conformal non-invariance of gravitons, and 1-loop finiteness of quantum gravity (QG). The effect is due to graviton-ghost condensates arising from the interference of quantum coherent states. The theory is constructed as follows: Faddeev-Popov-De Witt gauged path integral -> factorization of classical and quantum variables -> transition to the 1-loop approximation -> choice of ghost sector, satisfying 1-loop finiteness of the theory off the mass shell. The Bogolyubov-Born-Green-Kirckwood-Yvon (BBGKY) chain for the spectral function of gravitons renormalized by ghosts is used to build a theory of gravitons in the isotropic Universe. We found three exact solutions of the equations that describe virtual graviton and ghost condensates as well as condensates of instanton fluctuations. Exact solutions correspond to various condensates with different graviton-ghost compositions. The formalism of the BBGKY chain takes into account the contribution of non-relativistic matter in the formation of a common self-consistent gravitational field. It is shown that the era of non-relativistic matter dominance must be replaced by an era of dominance of graviton-ghost condensate. Pre-asymptotic state of DE is a condensate of virtual gravitons and ghosts with a constant conformal wavelength. The asymptotic state predicted by the theory is a graviton-ghost condensate of constant physical wavelength in the De Sitter space. Such DE phenomenon is presented in the form of the model that interpolates the exact solutions of equations of 1-loop QG. Processing of observational DE data extracted from the Hubble diagram for supernovae SNIa suggests that the graviton-ghost condensate is an adequate variable component of DE. 
Leonid Marochnik (1), Daniel Usikov, and Grigory Vereshkov (2) ((1)   University of Maryland, College Park, (2) Research Ins...