2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/135366From an operad C with an action of a group G, we construct new operads using the homotopy fixed point and orbit spectra. These new operads are shown to be equivalent when the generalized G-Tate cohomology of C is trivial. Applying this theory to the little disk operad C_2 (which is an S^1 operad) we obtain variations on Getzler's gravity operad, which we show governs the Chas-Sullivan string bracket.36 pages, 1 figure. Changes: main proofs and exposition streamlined, new section on continuous cohomology of operads, font changed. To appear in Math. AnnAlgebraic TopologyGeometric Topology55N91, 55P43, 55P92, 55R12, 14D22, 18D50text