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Part of higher category theory that for instance in Algebraic Topology enables us to capture finer homotopic distinctions. As in say Eilenberg-Maclane spaces.

7 votes
1 answer
748 views

What's a (infinity-) semi-stack?

A stack is an object that mixes the notions of (algebraic) space and group. The key insight of stack theory is that most things you would want to do with spaces you can do with stacks: namely, you hav …
Dmitry Vaintrob's user avatar
5 votes
1 answer
391 views

Homotopy limit of model categories in the category of categories

Say $$\mathcal{C'}\to \mathcal{C}\leftarrow \mathcal{D}$$ is a diagram of model categories and (e.g. Left) Quillen functors. I want to write down a (hopefully simple) model category $\mathcal{D}'$, or …
Dmitry Vaintrob's user avatar
2 votes
0 answers
115 views

Some operations on categories - nomenclature question

Suppose that we have a "diagram of categories", i.e. a map from some small category $J$, viewed as a 2-category (with trivial two-morphisms) to the category of categories, $j\mapsto \mathcal{C}_j.$ Th …
Dmitry Vaintrob's user avatar
6 votes
1 answer
236 views

Monochromatic infinity operads as algebras over the "operad operad"

In the "ordinary" operad category, it is known that there is a colored operad $Op$ with set of colors $\mathbb{N}$ corresponding to "degrees" of vertices and with operations indexed by trees, such tha …
Dmitry Vaintrob's user avatar
5 votes
1 answer
245 views

Model structure on wheeled topological properads

A wheeled properad is roughly, if I understand correctly, a properad (or PROP) with contraction maps $O_i^j\to O_{i-1}^{j-1}$ which contract an input with an output. There is a book, Infinity Properad …
Dmitry Vaintrob's user avatar
17 votes
2 answers
688 views

Homotopy theories of operads

I know of three homotopy theories of colored operads. The (derived) localization category of Berger-Moerdijk's model structure on the category of strict simplicial (or topological) operads, with wea …
Dmitry Vaintrob's user avatar
6 votes
0 answers
242 views

CoCartesian vs. locally CoCartesian fibrations

Say $\pi: C\to J$ is an inner fibration of $\infty$-categories. Then "morally", $\pi$ corresponds to a diagram indexed by $J$ in the "category of categories with correspondences", and if $\pi$ is coCa …
Dmitry Vaintrob's user avatar
7 votes
0 answers
215 views

Duality of Hopf algebras and duality of spectra

Let $S$ be the sphere spectrum, and for $X$ a topological space, let $S(X)$ be the mapping spectrum from the free loop spectrum on $X$ to the sphere spectrum. This is an $E_\infty$ ring spectrum (also …
Dmitry Vaintrob's user avatar
6 votes
0 answers
121 views

Recovering operad units from homotopy units

It is my understanding that the $\infty$-category of non-unital connected topological monoids is equivalent to the $\infty$-category of connected topological groups. It follows that the functor from u …
Dmitry Vaintrob's user avatar
8 votes
1 answer
975 views

Compactly supported sections of coherent sheaves and the dualizing complex

Suppose $U$ is a (possibly singular) scheme and $X$ is a compactification (potentially unnecessary at least in characteristic $0$). Let $\pi:X\to *$ be the map to the point (though one can consider mo …
Dmitry Vaintrob's user avatar
3 votes
0 answers
178 views

Twisting of the power functor

Let $k$ be a field of characteristic $p$ and $D^b(k)$ be the infinity (equivalently, DG) category of perfect complexes over $k$. Let $C_p(=\mathbb{Z}/p)$ be the cyclic group on $p$ elements. For a $C_ …
Dmitry Vaintrob's user avatar
2 votes
0 answers
75 views

Diagrammatic model for free product in monad infinity category

$\newcommand{\C}{\mathcal{C}}$ Suppose $M$ is a monad in an $\infty$-category $\C,$ and $A, B$ are two algebras over $M$. I'm willing to assume any reasonable "niceness" conditions on $\C$, $M$, etc: …
Dmitry Vaintrob's user avatar
11 votes
1 answer
778 views

Connectedness, loops and formal moduli problems

Let $k$ be an algebraically closed field of characteristic zero. Formalizing a classical folk concept, Pridham and (in a different way,) Lurie defined a formal moduli problem (over $k$) to be a functo …
Dmitry Vaintrob's user avatar