Multi-field open ination and instanton

In the open ination scenario, phase transition from false vacuum ination at a local minimum to slow-roll ination is mediated by the quantum tunneling. In this work, we present a concrete multi-field open ination model, explicitly showing how the bubble is nucleated by tunneling of scalar fields, and how slow-roll ination in the nucleated bubble follows. This model is the first viable open ination model with a simple potential. Multi-field tunneling is described by multi-field instanton method, which is an natural extension to the Coleman-De Luccia(CDL) instanton method. Evolution of the universe in the bubble obeys equations of motion for the open Friedmann- Lemaître-Robertson- Walker(FLRW) universe.