# nLab Ek-Algebras

### Context

#### Higher algebra

higher algebra

universal algebra

# Contents

## Idea

This are notes on

• Jacob Lurie, $\mathbb{E}[k]$-Algebras (pdf)

Using the definition of the notion (∞,1)-operad in terms of a vertical categorification of the notion of category of operators, the article discusses the $\mathbb{E}_k$- or little cubes operads and its En-algebras.

A major application in the second part of the article is the study of topological chiral homology.

## Definitions and results

### Grouplike monoid objects

Let $\mathcal{X}$ be an ∞-stack (∞,1)-topos and $X :$ Assoc $\to \mathcal{X}$ be a monoid object in $\mathcal{X}$. Say that $X$ is grouplike if the composite

$\Delta^{op} \to Ass \to \mathcal{X}$

(see 1.1.13 of Commutative Algebra)

is a groupoid object in $\mathcal{X}$.

Say an $\mathbb{E}[1]$-algebra object is grouplike if it is grouplike as an Assoc-monoid. Say that an $\mathbb{E}[k]$-algebra object in $\mathcal{X}$ is grouplike is the restriction along $\mathbb{E}[1] \hookrightarrow \mathbb{E}[k]$ is. Write

$Mon^{gp}_{\mathbb{E}[k]}(\mathcal{X}) \subset Mon_{\mathbb{E}[k]}(\mathcal{X})$

for the (∞,1)-category of grouplike $\mathbb{E}[k]$-monoid objects.

### Main result: $k$-fold delooping, monoidalness and $\mathbb{E}[k]$-action

The following result makes precise for parameterized ∞-groupoids – for ∞-stacks – the general statement that $k$-fold delooping provides a correspondence betwen n-categories that have trivial r-morphisms for $r \lt k$ and k-tuply monoidal n-categories.

###### Theorem (k-tuply monoidal $\infty$-stacks)

Let $k \gt 0$, let $\mathcal{X}$ be an ∞-stack (∞,1)-topos and let $\mathcal{X}_*^{\geq k}$ denote the full subcategory of the category $\mathcal{X}_{*}$ of pointed objects, spanned by those pointed objects thar are $k-1$-connected (i.e. their first $k$ ∞-stack homotopy groups) vanish. Then there is a canonical equivalence of (∞,1)-categories

$\mathcal{X}_*^{\geq k} \simeq Mon^{gp}_{\mathbb{E}[k]}(\mathcal{X}) \,.$
###### Proof

This is EKAlg, theorem 1.3.6..

Specifically for $\mathcal{X} = Top$, this reduces to the classical theorem by Peter May

###### Theorem (May recognition theorem)

Let $Y$ be a topological space equipped with an action of the little cubes operad $\mathcal{C}_k$ and suppose that $X$ is grouplike. Then $Y$ is homotopy equivalent to a $k$-fold loop space $\Omega^k X$ for some pointed topological space $X$.

###### Proof

This is EkAlg, theorem 1.3.16.

Lurie’s proof of the equivalence of $n+1$-connected objects with grouplike $E[k]$-objects is entirely at the level of (∞,1)-categories. One would hope that in addition there is a model for this equivalence at the level of model categories.

There is a model category structure on the category $Top_*$ of pointed topological spaces, such that the cofibrant objects are $n$-connected CW-complexes, described in

• J. I. Extremiana Aldana, Luis Javier Hernández Paricio? and
Maria Teresa Rivas Rodriguez, A closed model category for $(n-1)$-connected spaces , Proc. AMS, 124, Number 11, 1996 (pdf)

### Stabilization hypothesis

A proof of the stabilization hypothesis for k-tuply monoidal n-categories is a byproduct of corollary 1.1.10, stated as example 1.2.3

It has been long conjectured that it should be true that when suitably defined, there is a tensor product of $\infty$-operads such that

$\mathbb{E}_k \otimes \mathbb{E}_{k'} \simeq \mathbb{E}_{k + k'} \,.$

This is discussed and realized in section 1.2. The tensor product is defined in appendix B.7.

### Deligne conjecture

Section 2.5 gives a proof of a generalization of the Deligne conjecture.

category: reference

Revised on March 22, 2012 07:55:49 by Tim_Porter (95.147.237.122)