Rigidity of Totally Geodesic Hypersurfaces in Negative Curvature

Let $M$ be a closed hyperbolic manifold containing a totally geodesic hypersurface $S$, and let $N$ be a closed Riemannian manifold homotopy equivalent to $M$ with sectional curvature bounded above by $-1$. Then it follows from the work of Besson-Courtois-Gallot that ${\pi }_1(S)$ can be represented by a hypersurface $S^{\mathrm{\prime }}$ in $N$ with volume less than or equal to that of $S$. We study the equality case: if ${\pi }_1(S)$ cannot be represented by a hypersurface $S^{\mathrm{\prime }}$ in $N$ with volume strictly smaller than that of $S$, then must $N$ be isometric to $M$? We show that many such $S$ are rigid in the sense that the answer to this question is positive. On the other hand, we construct examples of $S$ for which the answer is negative.