Transmission and reflection coefficients for a scalar field inside a charged black hole

Using the late-time expansion we calculate the leading-order coefficients describing the evolution of a massless scalar field inside a Reissner-Nordström black hole. These coefficients may be interpreted as the reflection and transmission coefficients for scalar-field modes propagating from the event horizon to the Cauchy horizon. Our results agree with those obtained previously by Gursel et al. by a different method.