New Perspective on Cosmic Coincidence Problems

Cosmological data suggest that we live in an interesting period in the history of the universe when ρ_Λ∼ρ_M∼ρ_R. The occurrence of any epoch with such a “triple coincidence” is puzzling, while the question of why we happen to live during this special epoch is the “Why now?” problem. We introduce a framework which makes the triple coincidence inevitable; furthermore, the “Why now?” problem is transformed and greatly ameliorated. The framework assumes that the only relevant mass scales are the electroweak scale M_EW, and the Planck scale M_Pl and requires ρ_Λ^1/4∼M_EW²/M_Pl parametrically. Assuming that the true vacuum energy vanishes, we present a simple model, where a false vacuum energy yields a cosmological constant of this form.