The Unruh vacuum and the in-vacuum in the Reissner-Nordström spacetime

Abstract: The Unruh vacuum is widely used as quantum state to describe black hole evaporation since near the horizon it reproduces the physical state of a quantum field, the so called in-vacuum, in the case the black hole is formed by gravitational collapse. We examine the relation between these two quantum states in the background spacetime of a Reissner-Nordstr\"om black hole (both extremal and not) highlighting similarities and striking differences.