Nonmeasurability of the Quantum Numbers of a Black Hole

We consider neutral-meson (scalar and vector), electromagnetic, and neutrino quantum fields interacting with classical sources on a Schwarzschild background. The meson fields decouple from the source when it reaches r=2m. This means that the coupling constant is effectively set equal to zero at the horizon. Such a phenomenon does not happen for an electromagnetic field. The sharp difference between vector mesons of any mass and photons suggests that charged black holes can exist only if the photon mass is exactly zero. Neutrinos do not decouple from the source either, but the remaining coupling is given by an unobservable phase factor. These results provide further evidence in favor of Wheeler's conjecture that the only measurable quantum numbers of a black hole are mass, charge, and angular momentum and that, consequently, the laws of conservation of baryon and lepton number are "transcended" in black-hole physics.