We compute a Simons-type formula for the stress-energy tensor of biharmonic maps
from surfaces. Specializing to Riemannian immersions, we prove several rigidity
results for biharmonic CMC surfaces, putting in evidence the influence of the
Gaussian curvature on pseudoumbilicity. Finally the condition of biharmonicity is
shown to enable an extension of the classical Hopf theorem to CMC surfaces in any
ambient Riemannian manifold.
Keywords
biharmonic maps, constant mean curvature, stress-energy
tensor