# Graded multiplications on iterated bar constructions

## TL;DR

This paper develops a graded multiplication structure on iterated bar constructions within symmetric monoidal categories, ensuring good monoidal properties and broad applicability to various algebraic and topological contexts.

## Contribution

It introduces a new graded multiplication on iterated bar constructions that preserves monoidal structures in a broad categorical setting.

## Key findings

- Established monoidal properties of the geometric realization functor.
- Defined a graded multiplication on iterated bar constructions for ring objects.
- Applied the framework to simplicial sets, modules, topological spaces, chain complexes, and spectra.

## Abstract

We define a bar construction endofunctor on the category of commutative augmented monoids $A$ of a symmetric monoidal category $\mathcal{V}$ endowed with a left adjoint monoidal functor $F:s\mathbf{Set}\to \mathcal{V}$. To do this, we need to carefully examine the monoidal properties of the well-known (reduced) simplicial bar construction $B_\bullet(1,A,1)$. We define a geometric realization $|-|$ with respect to the image under $F$ of the canonical cosimplicial simplicial set. This guarantees good monoidal properties of $|-|$: it is monoidal, and given a left adjoint monoidal functor $G:\mathcal{V}\to \mathcal{W}$, there is a monoidal transformation $|G-|\Rightarrow G|-|$. We can then consider $BA=|B_\bullet A|$ and the iterations $B^nA$. We establish the existence of a graded multiplication on these objects, provided the category $\mathcal{V}$ is cartesian and $A$ is a ring object. The examples studied include simplicial sets and modules, topological spaces, chain complexes and spectra.