Brane Big - Bang Brought by Bulk

We propose an alternative inflationary universe scenario in the context of Randall-Sundrum braneworld cosmology. In this new scenario the existence of extra-dimension(s) plays an essential role. First, the brane universe is initially in the inflationary phase driven by the effective cosmological constant induced by small mismatch between the vacuum energy in the 5-dimensional bulk and the brane tension. This mismatch arises since the bulk is initially in a false vacuum. Then, the false vacuum decay occurs, nucleating a true vacuum bubble with negative energy inside the bulk. The nucleated bubble expands in the bulk and consequently hits the brane, bringing a hot big-bang brane universe of the Randall-Sundrum type. Here, the termination of the inflationary phase is due to the change of the bulk vacuum energy. The bubble kinetic energy heats up the universe. We derive the constraints on the model parameters taking into account the following requirements: the flatness of our universe, sufficiently high reheating temperature for the standard nucleosynthesis to work, and the validity of Newton’s law up to 1mm. We find that these constraints are satisfied in a wide range of the model parameters. To discuss the flatness problem, we develop a method to treat quantum tunneling on a space with boundary.