Effective state, Hawking radiation and quasi-normal modes for Kerr black
  holes
  The non-strictly continuous character of the Hawking radiation spectrum
generates a natural correspondence between Hawking radiation and black hole
(BH) quasi-normal modes (QNM). In this work, we generalize recent results on
this important issue to the framework of Kerr BHs (KBH). We show that also for
the KBH, QNMs can be naturally interpreted in terms of quantum levels. Thus,
the emission or absorption of a particle is in turn interpreted in terms of a
transition between two different levels. At the end of the paper, we also
generalize some concepts concerning the "effective state" of a KBH.
