Prediction of a finite bare electrical charge from quantum gravity

In the spirit of general relativity, spacetime should become curved due to the presence of a particle of a given mass and charge, We try to understand this fact in the quantum theory of a thin shell of matter. It leads to a generalization of the potential energy of the shell in the semiclassical highest dominant order of Planck mass. Rather surprisingly, the quantization of charge is obtained as a consequence of the existence of bound states and the quantum of the squared bare electrical charge is $\hbar c/2