McDonald, John
(2013)
*Explaining the dark energy, baryon and dark matter coincidence via domain-dependent random densities.*
Journal of Cosmology and Astroparticle Physics, 2013 (5).
ISSN 1475-7516

## Abstract

The dark energy, dark matter and baryon densities in the Universe are observed to be similar, with a factor of no more than 20 between the largest and smallest densities. We show that this coincidence can be understood via superhorizon domains of randomly varying densities when the baryon density at initial collapse of galaxy-forming perturbations is determined by anthropic selection. The baryon and dark matter densities are assumed to be dependent on random variables theta(d) and theta(b) according to rho(dm) proportional to theta(alpha)(d) and rho(b) proportional to theta(beta)(b), while the effectively constant dark energy density is dependent upon a random variable phi(Q) according to rho(Q) proportional to phi(n)(Q). The ratio of the baryon density to the dark energy density at initial collapse, r(Q), and the baryon-to-dark matter ratio, r, are then determined purely statistically, with no dependence on the anthropically-preferred baryon density. We compute the probability distribution for r(Q) and r and show that the observed values of r(Q) and r can be naturally understood within this framework. In particular, for the case alpha = 2, beta = 1 and n = 4, which can be physically realized via a combination of axion dark matter, Affleck-Dine baryogenesis and frozen quintessence with a phi(4)(Q) potential, the range of r(Q) and r which corresponds to the observed Universe is a quite natural, with a probability which is broadly similar to other ranges of r(Q) and r.