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

1 vote
1 answer
836 views

Homological equivalence for algebraic cycles

How does one prove that for a smooth projective variety $X$ over an algebraically closed field $k$, an algebraic cycle that is homologically equivalent to zero is also numerically equivalent to zero? …
Paul Graaf's user avatar
1 vote
1 answer
1k views

Birational maps and Picard groups

Suppose $X$ and $Y$ are curves, and suppose $f: Y \to X$ is a birational map. If $f$ is bijective on geometric points, what can be said about the induced map on the Picard groups $Pic(X) \to Pic(Y)$ …
Paul Graaf's user avatar
3 votes
1 answer
2k views

When does a finite morphism induce isomorphism on cohomology?

Let $Y \to X$ be a finite morphism of schemes of dimension $n$. The induced map on the top cohomology $H^n(X, \mathcal O_X) \to H^n(Y, \mathcal O_Y)$ is always surjective. When is it injective? Can …
Paul Graaf's user avatar
8 votes
1 answer
2k views

Line bundles and vector bundles on $\mathbb P^1 \times \mathbb P^1$

Is there a classification of vector bundles on $\mathbb P^1 \times \mathbb P^1$? I know that the analogue of Grothendieck's splitting theorem is not true for $\mathbb P^1 \times \mathbb P^1$. Is it …
Paul Graaf's user avatar