Absorption of massive scalar field by a charged black hole

The absorption of a quantum particle represented as a massive scalar field by a Reisner-Nordstrom black hole is investigated by observing how a certain reflection coefficient of the scalar wave changes in various cases. The radial wave equation in the Reisner-Nordstrom geometry is obtained from the wave equation for a charged scalar field, and it is shown that the reflection coefficient depends on the ratio of the Schwarzschild radius to the Compton wavelength. The absorption and reflection of a spherical wave by a small black hole is analyzed. It is found that the wave will be almost completely reflected in the low-energy case when the Schwarzschild radius is much less than the Compton wavelength and that almost total absorption occurs in the high-energy limit. It is also found that the wave will be amplified when the level-crossing condition is satisfied.