2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/76722We show that solutions of the Seiberg-Witten equations lead to non-trivial lower bounds for the L2-norm of the Weyl curvature of a compact Riemannian 4-manifold. These estimates are then used to derive new obstructions to the existence of Einstein metrics. These results considerably refine those previously obtained using scalar-curvature estimates alone.17 pages. LaTeX2e. Revised version improves estimates, simplifies proofs, and gives cleaner applicationsDifferential GeometryAlgebraic GeometryGeometric Topologytext