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Prime numbers, diophantine equations, diophantine approximations, analytic or algebraic number theory, arithmetic geometry, Galois theory, transcendental number theory, continued fractions

5 votes

Do there exist modern expositions of Klein's Icosahedron?

There is the outrageously expensive "Geometry of the quintic" by Jerry Shurman, which discusses both Klein and Doyle-McMullen approaches (and then some more).
David Lehavi's user avatar
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32 votes

Useless math that became useful

Fast Fourier transform: Originally developed by Gauss in early 19th century. Gauss thought it is unworthy of publication, because there were better computational techniques. It only appeared in his co …
David Lehavi's user avatar
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4 votes

If an abelian variety has an m-torsion point, is the set of all Galois conjugates of the m-t...

No. Take $E=Z(zy^2 = x(x^2+z^2))$, identifying zero with $(0:1:0)$. Then $(-1:0:1)$ is the only real non trivial 2-torsion point of $E(\mathbb{R})$.
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3 votes

Analysis of a quadratic diophantine equation

As Robin and Fedor observed the variety in question is a quartic Del Pezzo surface. There is a nice treatment in Igor Dolgachevs "Topics in classical algebraic geometry I" section 8.5 (including expli …
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3 votes

When is a product of elliptic curves isogenous to the Jacobian of a hyperelliptic curve?

With 2^2 isogeny it never works: F. Richelot, De transformatione integralium Abelianorum primi ordinis comentatio. J. reine angew. Math. 16 (1837) 221-341 G. Humbert, Sur la transformation ordinaire …
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2 votes

Modular curves of genus zero and normal forms for elliptic curves

The first thing you'd need in order to define a normal form is unirationality of the moduli space (otherwise you don't even have the correct number of parameters). In dimension 1, this means that you …
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3 votes
Accepted

Choosing a fast computer algebra system that works in characteristic p?

My personal experience is a few years old, but I don't think things have changed much. Sage is (or actually, was) more about ease of use then about performance. The only three CAS's you want to consid …
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6 votes

Geometry Vs Arithmetic of schemes

Look at Dan Abramovich's Birational geometry for number theorists
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9 votes

Etale cohomology -- Why study it?

One of the annoying aspects with sheaf cohomology in algebraic geometry is that - even for curves over the complex numbers - the cohomological dimensions are not what you want them to be, if you are u …
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1 vote

Can we count isogeny classes of abelian varieties?

For any genus, as long as you have non-ismorphic curves, you have non-isomorphic Abelian variety. For genus 2, you have the Honda-Tate theorem, giving the classes of Abelian varieties (and there is …
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6 votes

Proof of no rational point on Selmer's Curve $3x^3+4y^3+5z^3=0$

The "standard" technique for killing the Hasse priniciple for elliptic curves is to show that the Tate-Shafarevich group has a copy of (Z/mZ)^2 for some m - see chapter X in Silverman's the arithmetic …
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3 votes

Solving polynomial equations when you know in which number field the solutions live

I have to say that this sounds suspiciously close to Matiyasevich's proof of Hilbert's 10th problem (Yuri V. Matiyasevich, Hilbert's Tenth Problem, MIT Press, Cambridge, Massachusetts, 1993). The "yog …
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2 votes

Why are functional equations important?

Sometimes you get very concrete algebro-geometric facts from functional equations: Example 1: The functional equation relating Weierstrass P (for a lattice L in C) and it's derivative is the equation …
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