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

91 votes

Philosophy behind Mochizuki's work on the ABC conjecture

Last revision: 10/20. (Probably the last for at least some time to come: until Mochizuki uploads his revisions of IUTT-III and IUTT-IV. My apology for the multiple revisions. ) Completely rewritten. …
37 votes

Philosophy behind Mochizuki's work on the ABC conjecture

Let me also try to give, in a modest complement to Minhyong Kim's great post, some additional remarks on Mochizuki's strategy. The idea that has led to the development of "Inter-universal Teichmuller …
35 votes
Accepted

Are rational varieties simply connected?

Yes! (I assume it was implicit in your question that the variety be projective?) More generally: any smooth, complex, rationally connected projective variety is simply connected. See Debarre's book …
Vesselin Dimitrov's user avatar
26 votes

irreducibility of discriminant

The discriminant locus has the following geometric interpretation, given in the introductory chapter of [Gelfand, Kapranov, Zelevinsky: Discriminants, Resultants and Multidimensional Determinants]. L …
Vesselin Dimitrov's user avatar
13 votes

Smoothness of the "Archimedean special fiber" in Arakelov geometry

In Arakelov geometry, the conventional wisdom is that the ``closed fibre at $\infty$'' should be viewed as totally degenerate. This is the extreme opposite of smoothness. A visualization in the case o …
Vesselin Dimitrov's user avatar
13 votes

First formulation of the Dedekind and Hasse-Weil conjectures

Regarding the first of these conjectures, I believe it was first explicitly stated (in the more general setting of a relative extension $K/k$) in Artin's 1923 paper [Über die Zetafunktionen gewisser a …
Vesselin Dimitrov's user avatar
12 votes
Accepted

Mori: p-adic and real hemispheres of the mathematical universe?

As the night sky, mathematics has two hemispheres; the archimedean hemisphere and the non-archimedean hemisphere. For some reasons, the latter hemisphere is usually under the horizon of our world, …
Vesselin Dimitrov's user avatar
11 votes
Accepted

Nakai-Moishezon theorem for abelian varieties

On an abelian variety (regardless of the characteristic), an effective divisor with positive self-intersection is ample. To be more precise, it suffices here to recall that on any simple abelian varie …
Vesselin Dimitrov's user avatar
11 votes
1 answer
876 views

Higher Fano varieties and Tsen's theorem

The rational connectivity of (complex) Fano manifolds ($c_1(T_X) > 0$) is one of the major, and surely most memorable achievements of Mori's bend-and-break method. To this day, despite intensive work …
Vesselin Dimitrov's user avatar
10 votes

Points of elliptic curves over cyclotomic extensions

Since you ask more generally for results on $E(\mathbb{Q}^{\mathrm{ab}})$, let me expand my comment into a short answer. Amoroso and Dvornicich discovered (A lower bound on the height in abelian ext …
Vesselin Dimitrov's user avatar
10 votes
2 answers
717 views

The height of an orbit under rational self-maps

I have this basic question on which, strangely enough, the algebraic dynamics literature appears to be silent. But the question does not appear to be totally trivial or uninteresting to me - am I wron …
9 votes

What is the chromatic number of the "conic hypergraph" on a non-singular plane cubic?

You mean the six points to be distinct, of course (or not all six points to be the same point). Fixing the analytic identification $(\wp(z),\wp'(z))$ with $T = \mathbb{C}/\mathbb{\Lambda}$, the Abel- …
Vesselin Dimitrov's user avatar
9 votes
Accepted

Geometric Lang conjecture - reference

abx's comment was made while I was writing this, but I am posting it as an answer anyway. There has not been a proof of this conjecture of Lang, which remains a wide open problem. Lu and Miyaoka's pa …
Vesselin Dimitrov's user avatar
8 votes
0 answers
355 views

Does Stepanov's method extend to complete intersections?

Stepanov (circa 1970) created the polynomial method to limit the rational points of an algebraic curve over $\mathbb{F}_q$, leading to one of several alternative proofs of Weil's Riemann hypothesis fo …
Vesselin Dimitrov's user avatar
8 votes
3 answers
2k views

When are isotrivial families split by a finite base-change?

A well-known theorem of Grauert and Fischer states that a smooth proper family of complex manifolds is a locally trivial fibration as soon as all the fibers are isomorphic. It is also easy to obtain a …
Vesselin Dimitrov's user avatar

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