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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

2 votes
0 answers
73 views

What should I call a log scheme with free reduced monoids?

This is a terminology question about a class of log varieties. Given an fs (fine and saturated) log variety $(X, M)$ (for $M$ the defining sheaf of monoids), any geometric point $x\in X$ has a finitel …
Dmitry Vaintrob's user avatar
4 votes
0 answers
161 views

Is the Serre dualizing complex local in the analytic topology?

There is a Serre dualizing complex $S_X\in D^b Coh(X)$ for any scheme $X$ of finite type. For proper schemes, it is characterized as the sheaf defining the right adjoint to derived global sections, an …
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
4 votes
0 answers
115 views

Delta distributions that are smooth on strata of a singular manifold

This is a mild reformulation of a previous question. Let $R = C^\infty(\mathbb{R}^N)$ and let $I$ be an ideal in $R$ which cuts out an $n$-dimensional "singular $C^\infty$ manifold $X$" in $\mathbb{R} …
Dmitry Vaintrob's user avatar
8 votes

Number of points of algebraic curve

Edit The original diagonalization argument function I gave didn't satisfy the inequality. The following answer works. A diagonalization argument works here to show there aren't! Take an enumeration $X …
Dmitry Vaintrob's user avatar
6 votes
0 answers
94 views

forms on singular spaces that can be integrated on an LCI

I'd like to characterize rational $k$-forms on a singular scheme $X$ which can be integrated on any (real) bounded submanifold that is locally LCI in $X$ in a real sense (i.e., which is the real preim …
Dmitry Vaintrob's user avatar
10 votes
0 answers
340 views

Hodge structure and rational coefficients

Suppose $X$ is a complex projective variety with a model $X_\mathbb{Q}$ defined over the rational numbers. Then there is a rational de Rham lattice $H^k_{dR}(X_\mathbb{Q}, \mathbb{Q})\subset H^k(X, \m …
Dmitry Vaintrob's user avatar
1 vote

Separable extensions & topology vs inseparable extensions and algebra

I would guess that the intuition is that separable extensions extend uniquely over "infinitesimal thickenings", i.e. deformations over a nilpotent base. This makes their classification problem "rigid" …
Dmitry Vaintrob's user avatar
7 votes
1 answer
489 views

Localization of symmetric monoidal categories and geometry

I have a series of vague questions, related to localization of symmetric monoidal categories. Here is the context. Say we are working over a field of characteristic zero. Then the "one category leve …
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
4 votes
Accepted

Derived category of singular varieties

Let $\tilde{X}_k$ be the normalization of the closed $k$-codimension stratum, so $\tilde{X}_0$ is the normalization of $X$. Then there is a diagram of pullback functors between the categories $\text{P …
Dmitry Vaintrob's user avatar
5 votes
Accepted

Dimension of $\ell$-adic Eilenberg-Maclane space

I see this is one of your first question on MO -- welcome! The topic of the question is certainly interesting but I think you need to put a little more effort in future questions into being clear (fir …
Dmitry Vaintrob's user avatar
22 votes

Why is the Fourier transform so ubiquitous?

To add a representation theory perspective: if $G$ is a Lie group, and $f$ is a function (or more precisely a distribution) on $G$ then (under certain mild conditions on $f$ and $G$), the function $f$ …
Dmitry Vaintrob's user avatar
8 votes
1 answer
597 views

How much of the category of motives can be recovered from automorphisms of the Betti functor

Say we are working with schemes over a field $k\subset \mathbb{C}.$ A motive in the sense of Voevodsky is a functor $Sch\to D^bVect$ from (an appropriate category of) schemes to the DG category of com …
Dmitry Vaintrob's user avatar
2 votes
0 answers
212 views

Do dg schemes have derived points?

Working over a base field $k$ of characteristic $0$, say $K$ is a field (over $k$) and $X$ is a ("nice" if necessary) dg scheme in the sense of Toen-Vezzosi and others, and say $X^0$ is the reduced lo …
Dmitry Vaintrob's user avatar

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