Stability of extremal domains for the first eigenvalue of the Laplacian operator

In this paper, we compute the second variation of the first Dirichlet eigenvalue on extremal domains and establish criteria for stability. We classify the stable extremal domains in the 2-sphere and in higher-dimensional spheres when the boundary is minimal. We also prove topological bounds for stable domains with nonnegative total Gaussian curvature in a general compact Riemannian surface.