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

10 votes
0 answers
267 views

Looking for counterexamples: Are maximal tori in the automorphism groups of smooth complex q...

Let $X$ be a smooth quasiprojective variety over $\mathbb{C}$. It has a group of (algebraic) automorphisms $ \DeclareMathOperator{\Aut}{Aut} \Aut(X)$. Define a torus in $\Aut(X)$ to be a faithful alge …
Carlos Esparza's user avatar
5 votes
1 answer
439 views

Is the determinant line bundle of a coherent sheaf functorial (between sheaves of the same r...

The determinant line bundle of a coherent sheaf $\mathcal{F}$ on an $n$-dimensional (smooth) analytic space is defined as \begin{equation} \det \mathcal{F} := \bigotimes_i^n (\det \mathcal{E}_i)^{ …
Carlos Esparza's user avatar
11 votes
3 answers
1k views

Is every smooth projective variety contained in a chain of smooth projective varieties of in...

Let $X ⊆ \mathbb{P}^n$ be a smooth projective variety (over $\mathbb{C}$). I think we can find a chain of irreducible varieties $X = X_0 ⊆ X_1 ⊆ X_2 ⊆ \cdots ⊆ X_k = \mathbb{P}^n$ whose dimension incr …
Carlos Esparza's user avatar
6 votes
1 answer
569 views

Equivalent definitions of Kodaira dimension

The Kodaira($-$Iitaka) dimension of a line bundle $L$ on a complex manifold $X$ can be defined either in three ways: The maximal dimension of the image of the rational maps $φ_{|mL|} : X \dashrighta …
Carlos Esparza's user avatar
2 votes
0 answers
692 views

What algebraic condition corresponds to injectivity of a morphism of varieties?

$\DeclareMathOperator{\Spec}{Spec}$ Let $X = \Spec A$, $Y = \Spec B$ be affine complex varieties, that is reduced $\mathbb{C}$-schemes of finite type. Equivalently we can say that $A$ and $B$ are redu …
Carlos Esparza's user avatar
2 votes
1 answer
377 views

Are "transverse" hyperplane sections of nondegenerate irreducible projectice varieties alway...

Let $X \subseteq \mathbb{P}^n$ be a irreducible complex projective variety. It is called nondegenerate if it is not contained in a hyperplane in $\mathbb{P}^n$. Assuming $X$ is nondegenerate and irred …
Carlos Esparza's user avatar