Questions tagged [line-bundles]
A continuously varying family of one-dimensional vector spaces over a topological space. A related tag is the vector-bundles tag.
231 questions
4
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2
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482
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Vague question on $Pic^0$
For a smooth variety $X$ when $Pic^0(X)$ is trivial, we get an isomorphism between $N^1(X)$ and Picard group and life become easier.
My question is whether in general there are theorems, criteria ... ...
8
votes
1
answer
394
views
Pullback along the Torelli map is an isomorphism
I've been told many times that the Torelli map $J:\mathcal{M}_g\to \mathcal{A}_g$ for ($g\geq 2$, and at least on the level of coarse moduli spaces, over $\mathbb{C}$) gives an isomorphism of Picard ...
- 16k
10
votes
0
answers
526
views
Deformations of some simple quotient stacks.
I am interested in stacks of vector bundles on varieties and how deformations of the variety (including non-commutative ones) reflect themselves in deformations of the stack of vector bundles.
I will ...
- 1,180
6
votes
1
answer
640
views
A line bundle not big but with good intersection numbers
Let $X$ be a complex projective manifold of complex dimension $n$ and $A\to X$ an ample line bundle. Let $L\to X$ be a line bundle such that
$$
c_1(L)^k\cdot c_1(A)^{n-k}>0,\quad k=1,\dots,n.
$$
Is ...
- 7,902
2
votes
1
answer
424
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Different ways to construct maps and the tensor products of line bundles
Let $C$ be a curve. Then I know of two ways to create morphisms. To get morphisms from $C$, take a line bundle of any degree $L$ and use the linear system it determines to get a map into projective ...
- 16k
3
votes
1
answer
637
views
Can the class of the canonical bundle be recovered from the total space of the cotangent bundle if one forgets that it is a cotangent bundle?
This is a somewhat speculative question, so bear with that (or not, as is your preference).
Let $X$ be a smooth projective variety, and let $\omega_X$ be its canonical sheaf. The Euler class of ...
- 44.7k
5
votes
1
answer
527
views
graded ring associated to a line bundle in a tensor category
Let $\mathcal{A}$ be an abelian tensor category with unit $\mathcal{O}$. An object $\mathcal{L}$ is called invertible or a line bundle if there is some $\mathcal{L}^{-1}$ such that $\mathcal{L} \...
- 63.1k
4
votes
2
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825
views
finite-dimensionality of cohomology groups on compact riemann surfaces
does the finite dimensionlity of the first cohomology group ($ H^1 $) of the sheaf of meromorphic sections of a holomorphic line bundle on a compact riemann surface follow easily from the finite ...
- 73
5
votes
1
answer
630
views
Line bundles in abelian $\otimes$-categories
By an abelian $\otimes$-category I mean a symmetric monoidal category $(\mathcal{A},\otimes,\mathcal{O})$, such that $\mathcal{A}$ also is an abelian category and for every $M \in \mathcal{A}$ the ...
- 63.1k
21
votes
3
answers
8k
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Total space of the line bundle $\mathcal{O}(1)$ over $\mathbb{P}^n$
It is well known that total space of the tautological line bundle $\mathcal{O}(-1)$ over projective space $\mathbb{P}^n$ is closed subvariety of $\mathbb{P}^n\times\mathbb{A}^{n+1}$. My question is ...
- 525
4
votes
1
answer
1k
views
Tensor product of a line bundle with a large multiple of another positive line bundle also positive?
Let $X$ be a complex manifold and $\mathcal{L}$ be a positive line bundle on $X$. If $E$ is any other line bundle on $X$, then is it true that for all sufficiently large $m$, $\mathcal{L}^m \otimes E$ ...
- 5,359
5
votes
2
answers
5k
views
Technique to prove basepoint-freeness
Let $X$ be a smooth projective variety over $\mathbb{C}$.
And let $L$ be a big and nef line bundle on $X$.
I want to prove $L$ is semi-ample($L^m$ is basepoint-free for some $m > 0$).
The only way ...
- 627
8
votes
1
answer
952
views
volume of big line bundles under finite morphisms
Let $X$, $Y$ be complex projective varieties of dimension $n$, let $f:X \rightarrow Y$ be a surjective finite morphism of degree $d$ and let $B$ be a big line bundle on $Y$.
Is that true that vol($f^*...
- 205
6
votes
2
answers
851
views
What kind of line bundles have Chern class of Hodge type (2,0) or (0,2)?
If $L$ is a complex line bundle on a topological space $X$, let $c_1(L)$ denote the image of its Chern class in $H^2(X;C)$. A complex manifold structure on $X$ [ok which is also compact and say ...
- 4,949
6
votes
6
answers
5k
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What does the ample cone look like?
For a variety $X/k$, consider the monoid $A$ of classes of ample line bundles in $NS(X)$. What does $A \otimes_\mathbf{Z} \mathbf{R} \subset NS(X)_\mathbf{R}$ look like?
user19475
17
votes
2
answers
1k
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Line bundles vs. Cartier divisors on a non-integral scheme
It is well-known that if $X$ is an integral scheme, then there is an isomorphism $CaCl(X)\to Pic(X)$ taking $[D]$ to $[\mathcal{O}_X(D)]$. Does anyone know any simple examples where the above map ...
- 11.6k
4
votes
2
answers
1k
views
For a line bundle L on a smooth projective variety X, what is meant by Pic^L(X)
Hi everyone,
Let $X$ be a smooth projective variety over a field $k$ and let $L$ be a line bundle on $X$. I'm reading the article Heights for line bundles on arithmetic varieties and there one ...
- 9,497
4
votes
1
answer
1k
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Line Bundles on Torus Quotient
Suppose you have a scheme $X$ that is acted on by a torus $T$. Then the action induces a grading on the functions on $X$ by the character lattice of $T$. So for a fixed character $\lambda$, we can ...
- 5,548
6
votes
1
answer
2k
views
Line bundles: from transition functions to divisors
Recently I was thinking about how local systems are the same thing as vector bundles with flat connection, and how representations of the fundamental group gave rise to vector bundles. This got me ...
- 2,168
5
votes
2
answers
720
views
Relationship between Line Bundles with isomorphic ring of sections
Suppose two positive holomorphic line bundles $L_1 \to X_1, L_2\to X_2$ over two projective complex manifold $X_1, X_2$ have isomorphic ring of sections $R=R_1=R_2$ where $R_i=\oplus_{m=0}^\infty\...
user2529
1
vote
3
answers
999
views
On the Clifford index of a curve
Let X be an algebraic curve and c be the Clifford index of X.
When c is small (e.g c=1), what is the classification of the line bundle who computes c?
- 11
8
votes
3
answers
2k
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Holomorphic and antiholomorphic forms of projective space
For $\mathbb{CP}^1$ the bundles of holomorphic and antiholomorphic forms are equal to the $\mathcal{O}(-2)$ and $\mathcal{O}(2)$ respectively. Do the holomorphic and antiholomorphic bundles of $\...
- 3,409
3
votes
3
answers
687
views
Nature of Invertible Sheaves in which there are no global sections.
EDIT: Let me try to make the question clearer.
Consider the invertible sheaves $\mathcal{O}(d)$ over the projective space $\mathbb{P}^n$ where $d\in \mathbb{Z}$. Now, if $d>0$, among many ...
- 2,132
4
votes
1
answer
988
views
Torsion line bundles with non-vanishing cohomology on smooth ACM surfaces
I am looking for an example of a smooth surface $X$ with a fixed very ample $\mathcal O_X(1)$ such that $H^1(\mathcal O(k))=0$ for all $k$
(such thing is called an ACM surface, I think) and a globally ...
- 30.6k
7
votes
5
answers
3k
views
Indexing the line bundles over a Grassmannian.
As is well known, the line bundles over *CP*$^1$ are indexed by the integers. My question is how are the line bundles over *CP*$^n$, $n > 1$, and *Gr*$(n,k)$ indexed? Moreover, do there exist any ...
- 3,409
8
votes
2
answers
1k
views
Going further on How sections of line bundles rule maps into projective spaces
My question is located in trying to follow the argument bellow.
Given a normal algebraic variety $X$, and a line bundle $\mathcal{L}\rightarrow X$ which is ample, then eventually such a line bundle ...
- 2,132
23
votes
5
answers
10k
views
Maps to projective space determined by a line bundle
The following should be pretty standard for any algebraic geometer.
Let $X$ be a compact complex variety, and let $L$ be a line bundle on $X$. We say $L$ is 'generated by global sections' if for ...
- 13k
5
votes
4
answers
667
views
Sections of a divisor on elliptic curve
I'm interested in producing explicit bases for the sections of a line bundle on an embedded genus 1 curve. Let me restrict to the first case that I don't know how to do, so that I can be as concrete ...
- 2,955
17
votes
5
answers
2k
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What do gerbes and complex powers of line bundles have to do with each other?
We all know how to take integer tensor powers of line bundles. I claim that one should be able to also take fractional or even complex powers of line bundles. These might not be line bundles, but ...
- 44.7k
13
votes
3
answers
3k
views
What is the Theorem of the Cube?
What is the "theorem of the cube" for abelian varieties? What is the statement and how should I think about it?
- 27.5k
20
votes
2
answers
10k
views
does a line bundle always have a degree
For curves there is a very simple notion of degree of a line bundle or equivalently of a Weil or Cartier divisor. Even in any projective space $\mathbb P(V)$ divisors are cut out by hypersurfaces ...
- 3,968