Seifert hypersurfaces of 2-knots and Chern-Simons functional

For a given smooth $2$-knot in $S^4$, we relate the existence of a smooth Seifert hypersurface of a certain class to the existence of irreducible $SU(2)$-representations of its knot group. For example, we see that any smooth $2$-knot having the Poincar'e homology $3$-sphere as a Seifert hypersurface has at least four irreducible $SU(2)$-representations of its knot group. This result is false in the topological category. The proof uses a quantitative formulation of instanton Floer homology. Using similar techniques, we also obtain similar results about codimension-$1$ embeddings of homology $3$-spheres into closed definite $4$-manifolds and a fixed point type theorem for instanton Floer homology.