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

2 votes

Do finitely many plurigenera determine the Kodaira dimension?

I guess in general the answer is NO. For instance if you take $X$ to be an $n$ dimensional variety which is $Y\times E$, where $E$ is an elliptic curve and $Y$ is an $n-1$ dimensional variety of gen …
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1 vote

Does an essential resolution of 2-dimensional hypersurface singularity preserves

The answer is surely no. If $D$ itself does not have a minimal log smooth resolution, then certainly $(V,D)$ couldn't have such a log resolution you need. On the other hand, there are bunch of isolat …
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  • 656
12 votes
3 answers
1k views

Bertini's theorem in char p for base point free linear system

I always believed the following statement: if $X$ is a smooth variety over an algebraically closed field of positive characteristic, assuming we know that the general member of a base point free linea …
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4 votes

The minimal model program and symplectic resolutions

The answer to the first question: if $X$ has klt singularities, then there exists a $\mathbb{Q}$-factorial variety $Y$ with a birational morphism $\pi: Y\to X$, such that if you write $\pi^*K_X=K_Y+\ …
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2 votes
Accepted

blow-ups and singularities

I think this is true. Taking a point $x\in X$, and base change your setting up to its formal neighborhood, we can assume $K(X)\subset K(Y)$ is a Galois extension with finite abelian group. Now we can …
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20 votes

Open problems in Birational Geometry, after BCHM

Let me add my answer. In characteristic 0. Abundance conjecture. This is probably universally accepted as the most important question for the current minimal model program after BHCM's proof of finit …
4 votes
Accepted

Are weak Fano 4-folds with canonical Gorenstein singularities bounded?

If you further assume $X$ only has canonical singularity, and $-K_X$ is ample, then for any dimension, this is proved in ACC for log canonical thresholds Corollary 1.8. If you only assume $-K_X$ is …
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6 votes
Accepted

Possible singularities of the base of a Mori fiber space

Under the assumption that $X$ is $\mathbb{Q}$-factorial, section 5 of the paper https://arxiv.org/pdf/math/0606666 addressed this issue, which was also proved earlier in Ambro's paper. Basically, if y …
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  • 656
2 votes
1 answer
298 views

Lifting vector fields to its resolution in char $p$

In this paper 4.7, the authors showed that on a normal variety $X$, if there is a tangent vector field on its smooth locus, then it can be lifted as a logarithmic tangent vector field on a log resolu …
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8 votes
Accepted

Minimal Model Program for surfaces over algebraically closed fields of characteristic p

In the surface case, MMP in char p is known. See Koll'ar-Kov'ac's preprint on Koll'ar's webpage. In dimensional 3, the existence of divisorial contractions and flipping contractions is known as EWM ( …
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3 votes

Numerically negative exceptional divisor on a surface.

See the proof ON ISOLATED RATIONAL SINGULARITIES OF SURFACES (Artin) Propostiion 2 (i).
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