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Homotopy theory is an important sub-field of algebraic topology. It is mainly concerned with the properties and structures of spaces which are invariant under homotopy. Chief among these are the homotopy groups of spaces, specifically those of spheres. Homotopy theory includes a broad set of ideas and techniques, such as cohomology theories, spectra and stable homotopy theory, model categories, spectral sequences, and classifying spaces.

13 votes
2 answers
1k views

Correspondence between operads and $\infty$-operads with one object

Given a simplicial operad one can form its category of operators. This is a simplicial category with a functor to the category of finite pointed sets which is a bijection on objects and whose hom-spac …
Justin Noel's user avatar
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10 votes
1 answer
556 views

Loops and suspensions of higher categories

Given a pointed $(\infty,n)$-category $\mathcal{C}$, one can define the suspension of $\mathcal{C}$, $\Sigma\mathcal{C}$, via the homotopy pushout of $$\ast\leftarrow \mathcal{C}\rightarrow \ast.$$ Du …
Justin Noel's user avatar
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8 votes

$RO(G)$-graded homotopy groups vs. Mackey functors

I can answer your first question in some special cases. Let $p$ be a prime and $G=C_p$ the cyclic group of order $p$. If $p=2$, the answer to your question is yes and if $p$ is odd, then it is no. …
Justin Noel's user avatar
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5 votes
Accepted

The homotopy of universal Thom spectrum

Assume that $R$ is a connective $E_\infty$ ring spectrum. Typically $GL_1(R)$ denotes the set of components in $\Omega^\infty R$ which span $GL_1(\pi_0 R)=\pi_0 R^\times$. I would call the unit compon …
Justin Noel's user avatar
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4 votes

Group actions in a homotopy category

The spectral sequence I constructed with Niles Johnson was precisely designed to handle questions of this sort (here is a version that is closer to the publication version: T-algebra SS). A special ca …
Justin Noel's user avatar
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4 votes
Accepted

Loops and suspensions of higher categories

First let me thank Urs, Karol, and Rune Haugseng for helpful comments. Now note that the inclusion, $i$, of $\infty$-groupoids into $(\infty,n)$-categories has an $\infty$-categorical left adjoint, $ …
Justin Noel's user avatar
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4 votes

Weak operad and deloopings

Some clarifications: 1) You need that $X$ is grouplike (so the induced multiplication makes $\pi_0 X$ a group). This condition is always satisfied for a loop space, but not satisfied by the discrete …
Justin Noel's user avatar
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