Instantons on Cylindrical Manifolds

We consider an instanton,$\textbf{A}$,with $L^{2}$-curvature $F_{\textbf{A}}$ on the cylindrical manifold $Z=\mathbf{R}\times M$,where $M$ is a closed Riemannian $n$-manifold, $n\geq 4$.We assume $M$ admits a $3$-form $P$ and a $4$-form $Q$ satisfy $dP=4Q$ and $d\ast{Q}=(n-3)\ast P$.Manifolds with these forms include nearly K\"{a}hler 6-manifolds and nearly parallel $G_{2}$-manifolds in dimension 7.Then we can prove that the instanton must be a flat connection.