Speaker
Description
The present acceleration of the Universe can be sourced by the continuous generation of an energy density $\rho_b$ associated with a certain field $\varphi_b$. This idea is implemented by adding a new tensor term to Einstein equation. The creation process requires $\rho_b\neq 0$ as an initial condition, which is enforced by identifying $\varphi_b$ with the axion of a hidden gauge group that confined in recent cosmological times. Shortly before matter-dark energy equality, this led to a level crossing between $\varphi_b$ and the QCD axion, assumed to comprise dark matter. A small fraction of QCD axions converts into $\varphi_b$, generating the initial $\rho_b$ needed to trigger the creation process, offering a solution to the coincidence puzzle.
