On a Riemannian manifold $\bar{ M}^{ m+n}$ with an $(m+1)$-calibration $\Omega$, we prove that an $m$-submanifold $M$ with constant mean curvature $H$ and calibrated extended tangent space $\mathbb{ R}H\oplus TM$ is a critical point of the area functional for variations that preserve the enclosed $\Omega$-volume. This recovers the case described by Barbosa, do Carmo and Eschenburg, when $n=1$ and $\Omega$ is the volume element of $\bar{ M}$. To the second variation we associate an $\Omega$-Jacobi operator and define $\Omega$-stablility. Under natural conditions, we prove that the Euclidean $m$-spheres are the unique $\Omega$-stable submanifolds of $\mathbb{ R}^{ m+n}$. We study the $\Omega$-stability of geodesic $m$-spheres of a fibred space form $M^{ m+n}$ with totally geodesic $(m+1)$-dimensional fibres.
Categories: math.DG math-ph math.MP