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

7 votes

Infinitesimal deformations of the formal group of $\mathbb{G}_m$

This isn't a complete answer, but I think the general case is subtle. If $R\supset\mathbf{Q}$ is (pro-)artinian, then [SGA 3, VIIB 3.2] tells us that formal groups over $R$ are uniquely determined b …
Daniel Miller's user avatar
22 votes
Accepted

Is a locally free sheaf projective in the category of $\mathcal{O}_X$-modules when $X$ is an...

This answer is inspired by the discussion at this question. Let $X$ be an integral affine scheme admitting an open cover $X=U\cup V$ with $U$, $V$ and $X$ all distinct. I claim that $\mathscr O_X$ is …
Community's user avatar
  • 1
3 votes
0 answers
247 views

K-theory of categories of group schemes and abelian varieties

Let $k$ be a field (perfect, or characteristic zero if you want - I'm especially interested in when $k$ is a number field). Consider the categories $\mathsf{G}_k=\{\text{commutative affine group schem …
8 votes
2 answers
965 views

When does the categorical definition of a module work?

$\DeclareMathOperator{\ab}{Ab}\DeclareMathOperator{\qcoh}{QCoh}$ This entry in the nlab shows that for $A$ a (commutative unital) ring, the category $\mathsf{Mod}_A$ of $A$-modules is equivalent to th …
5 votes

Category of sheaves on the topological space X

$\DeclareMathOperator{\sh}{Sh}\DeclareMathOperator{\psh}{PSh}$ A1. Not especially. Essentially, one uses the fact that $\psh(X)$ is abelian (which is essentially trivial to prove) and then the sheafif …
Daniel Miller's user avatar