Classification of Solutions to a Critical Fourth-Order Equation on Complete Non-compact Manifolds
We study the critical biharmonic equation \[ \Delta^2 u=u^{\frac{n+4}{n-4}}, \] on a complete, connected, and non-compact Riemannian manifold \((M^n,g)\) of dimension \(n\geq 5\) with non-negative Ricci curvature. We establish an optimal pointwise second-order derivative estimate by Bernstein's method and the continuit...