1301.4189 (John McDonald)

Explaining the Dark Energy, Baryon and Dark Matter Coincidence via Domain-Dependent Random Densities    [PDF]

John McDonald

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} ~ \theta_{d}^{\alpha} and \rho_{b} ~ \theta_{b}^{\beta}, while the effectively constant dark energy density is dependent upon a random variable \phi_{Q} according to \rho_{Q} ~ \phi_{Q}^{n}. 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_{Q}^4 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.

View original: http://arxiv.org/abs/1301.4189