that argues that the relaxation time "TAU" of a physical system is never smaller than a bound:
TAU >= BETA / PI
where BETA is the inverse temperature. Black holes may saturate it. In terms of quasinormal frequencies, there must exist a quasinormal frequency whose imaginary part satisfies
PI . TEMPERATURE >= Im (OMEGA)
which is obtained by inverting the previous inequality. I feel that there should exist a proof. The temperature kind of causes the quasinormal modes to be periodic in "Im (OMEGA)" with the period "2.PI.TEMPERATURE", and there should exist a mode in the lower half of the horizontal periodic strip. Can you complete the proof?