  Gauge symmetries generally appear as a constraint algebra, under which one
expects all physical states to be singlets. However, quantum anomalies and
boundary conditions introduce central charges and change this picture, thus
causing gauge/diffeomorphism modes to become physical. We expose a
cohomological (Higgs-less) generation of mass in U(N)-gauge invariant
Yang-Mills theories through non-trivial representations of the gauge group.
This situation is also present in black hole evaporation, where the Virasoro
algebra turns out to be the relevant subalgebra of surface deformations of the
horizon of an arbitrary black hole.
