Unified Dark Energy and Dark Matter from Dynamical Spacetime Cosmology

Abstract: A model of unified dark matter and dark energy based on a Dynamical Spacetime Theory (DST) is studied. By introducing a Dynamical Spacetime vector field $\chi_\mu$, a conservation of an energy momentum tensor $T^{\mu\nu}_{(\chi)}$ emerges. The action allows for two different potentials, while one represents a dark energy. For constant potentials, the cosmological solution yields a non singular bouncing solutions that rapidly approaches the $\Lambda$CDM model. The Dynamical Time corresponds to the cosmic time as well. The theory fits with the late time expansion data of the Universe. With higher dimensions a mechanism for inflation and compactification appears, with exponential growth for some dimensions and exponential contraction of the others. By demanding that the Dynamical Spacetime vector field be a gradient of a scalar the DST becomes a theory with diffusive interacting, which asymptotically returns to the $\Lambda$CDM model as a stable point. These formulations lead to scenarios which address our understanding about the origin of the Universe.