Dear Stephen,
Thanks for your comments. Yes, page constraints limits description of what prompted each equation. On the other hand, after a rigorous definition of the quantum problem, I used a standard method of calculation in quantum mechanics following the textbook by Sakurai. Concerning the line of thinking that gave me the approach to this problem, and guided me through the application of the equations used, actually, I started to work on the problem of black hole quantum levels from two years. I had the intuition to replace the Hawking temperature with the effective temperature in order to take into account the non-strictly thermal character of the radiation spectrum in my paper JHEP 1108, 101 (2011). After this, I refined my results in my Essay Int. Journ. Mod. Phys. D 21, 1242023 (2012), which received an honorable mention in the 2012 Essay Competition of the Gravity Research Foundation, by discussing in detail the correspondence between Hawking radiation and BH QNMs. This winter, I had another intuition, i.e. that energies of Hawking quanta should be proportional to the effective temperature instead of to the Hawking temperature in case of deviation from the strict thermality of the radiation spectrum. At that point, by interpreting the absolute values of the QNMs in terms of total emitted energies, and, in turn, in terms of quantum levels, I developed my Essay by using standard techniques of quantum mechanics.
Cheers,
Ch.
P.S.
I checked eq. (22), it should be the same writing exp - (...) rather than exp(-...), or not?
P.P.S.
I am going to read your Essay in next days.