BRST nilpotence
= BRST nilpotence
{c}
{title2=$Q^2=0$}
A <BRST charge> is nilpotent when $Q^2=0$, making <BRST cohomology> well-defined. For the critical <bosonic string theory>, the matter and ghost <central charges> cancel, $D-26=0$, and the intercept is one. In a ghost convention with a zero-mode linear shift, the shifted total constraint generators, rather than the unshifted ones, obey the centerless <Witt algebra>.