Curved algebras are a generalization of differential graded algebras which have found numerous applications recently. The goal of this foundational article is to introduce the notion of a curved operad, and to develop the operadic calculus at this new level. The algebraic side of the curved operadic calculus provides us with universal constructions: using a new notion of curved operadic bimodules, we construct curved universal enveloping algebras. Since there is no notion of quasi-isomorphism in the curved context, we develop the homotopy theory of curved operads using new methods. This approach leads us to introduce the new notion of a curved absolute operad, which is the notion Koszul dual to counital cooperads nonnecessarily conilpotent, and we construct a complete Bar-Cobar adjunction between them. We endow curved absolute operads with a suitable model category structure. We establish a magical square of duality functors which intertwines this complete Bar-Cobar construction with the Bar-Cobar adjunction between unital operads and conilpotent curved cooperads. This allows us to compute minimal cofibrant resolutions for various curved absolute operads. Using the complete Bar construction, we show a general Homotopy Transfer Theorem for curved algebras. Along the way, we construct the cofree cooperad not necessarily conilpotent.
CONTENTSIntroduction 1 1. Recollections on different types of (co)operads 6 2. Curved operads and their curved algebras 13 3. Curved bimodules and universal functors 17 4. Curved cooperads and curved partial cooperads 23 5. The groupoid-colored level 25 6. Curved twisting morphisms and Bar-Cobar adjunctions at the operadic level 38 7. Counital partial cooperads up to homotopy and transfer of model structures 48 8. Duality functors and Koszul duality 53 9. Application: Homotopy transfer theorem for curved algebras 59 10. Appendix: What is an absolute partial operad ? 63 References 71