What simplified models say about unitarity and gravitational collapse

This paper reviews some work on the quantum collapse of the spherically sym metric gravitating thin shell of zero rest mass. Recent results on Kuchar d ecomposition are applied. The constructed version of quantum mechanics is u nitary, although the shell falls under its Schwarzschild radius if its ener gy is high enough. Rather that a permanent black hole, something like a tra nsient black and white hole pair seems to be created in such a case.