Moment categories and operads

Abstract

A moment category is endowed with a distinguished set of split idempotents, called moments, which can be transported along morphisms. Equivalently, a moment category is a category with an active/inert factorisation system fulfilling two simple axioms. These axioms imply that the moments of a fixed object form a monoid, actually a left regular band. Each locally finite unital moment category defines a specific type of operad which records the combinatorics of partitioning moments into elementary ones. In this way the notions of symmetric, non-symmetric and $n$-operad correspond to unital moment structures on $\Gamma$, $\Delta$ and ${\Theta }_n$ respectively. There is an analog of the plus construction of Baez-Dolan taking a unital moment category $\mathbb{C}$ to a unital hypermoment category ${\mathbb{C}}^{+}$. Under this construction, $\mathbb{C}$-operads get identified with ${\mathbb{C}}^{+}$-monoids, i.e. presheaves on ${\mathbb{C}}^{+}$ satisfying strict Segal conditions. We show that the plus construction of Segal's category $\Gamma$ embeds into the dendroidal category $\Omega$ of Moerdijk-Weiss.

Final version

Cited by in corpus (1)

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