Analytic Study of Rotating Black-Hole Quasinormal Modes

A Bohr-Sommerfeld equation is derived for the highly-damped quasinormal mode frequencies omega(n>>1) of rotating black holes. It may be written as 2\int_C(p_r+ip_0)dr=(n+1/2)h, where p_r is the canonical momentum conjugate to the radial coordinate r along null geodesics of energy hbaromega and angular momentum hbarm, p_0=O(omega^0), and the contour C connects two complex turning points of p_r. The solutions are omega(n) = - momega_0 - i(phi + ndelta), where {omega_0,delta}>0 are functions of the black-hole parameters alone. Some physical implications are discussed.