Integrability and BRST invariance from BF topological theory

Abstract

We consider the BRST invariant effective action of the non-abelian BF topological theory in $1+1$ dimensions with gauge group $Sl(2,\mathbb{R})$. By considering different gauge fixing conditions, the zero-curvature field equation give rise to several well known integrable equations. We prove that each integrable equation together with the associated ghost field evolution equation, obtained from the BF theory, is a BRST invariant system with an infinite sequence of BRST invariant conserved quantities. We construct explicitly the systems and the BRST transformation laws for the KdV sequence (including the KdV, mKdV and CKdV equations) and Harry Dym integrable equation.