Greybody factors at large imaginary frequencies

TL;DR

This paper calculates greybody factors for scalar and gravitational wave scattering by black holes at large imaginary frequencies, revealing a structure that may have a dual description involving black hole horizons.

Contribution

It extends previous work to compute transmission and reflection coefficients at large imaginary frequencies for various black holes, suggesting a possible duality involving horizons.

Findings

Transmission coefficients have a specific structure at large imaginary frequencies.

Results imply a dual description involving both horizons in Reissner-Nordstrom black holes.

Numerical evidence supports earlier theoretical formulas.

Abstract

Extending a computation which appeared recently in hep-th/0301173, we compute the transmission and reflection coefficients for massless uncharged scalars and gravitational waves scattered by d>=4 Schwarzschild or d=4 Reissner-Nordstrom black holes, in the limit of large imaginary frequencies. The transmission coefficient has an interpretation as the "greybody factor" which determines the spectrum of Hawking radiation. The result has an interesting structure and we speculate that it may admit a simple dual description; curiously, for Reissner-Nordstrom the result suggests that this dual description should involve both the inner and outer horizons. We also discuss some numerical evidence in favor of the formulas of hep-th/0301173.