The invariant charges of the Nambu-Goto String and Canonical Quantization
arXiv:hep-th/0403108 · doi:10.1063/1.1776644
Abstract
It is shown that the algebra of diffeomorphism-invariant charges of the Nambu-Goto string cannot be quantized in the framework of canonical quantization. The argument is shown to be independent of the dimension of the underlying Minkowski space.
v2: reference added