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Prime numbers, diophantine equations, diophantine approximations, analytic or algebraic number theory, arithmetic geometry, Galois theory, transcendental number theory, continued fractions
7
votes
Rational zeros of a polynomial
The polynomial defines a genus 2 curve. Your curve is birational to the genus two curve $C$ given by
$y^2=x^5+7x^4+18x^3+24x^2+16x+4$.
This curves has two rational Weierstrass points. These points cor …
12
votes
Computing factorials modulo p^N
I believe that the question whether $(p-1)! \bmod p^2$ is computable in polynomial time is still open. The best I am aware of is $O(p^{1/2+\epsilon})$, but I am not a specialist on this issue.
The co …
12
votes
Accepted
Counterexample to Proposition of Granville related to abc conjecture
I checked the proof of Granville. The proof only yields the bound
$\max \{ \deg(r),\deg(s)\}(\deg(G)-2)\}+1$
which covers your counterexample.
To be more detailed: The polynomials $r,s$ yield a morph …
4
votes
Non-coprime solutions to x^n+y^n = z^2
The answer to the question depends on the parity of $n$.
Suppose that $n=2k$ is even. Let $(x,y,z)$ be a nonzero solution to your equation, with $y\neq 0$.
Then $(x/y,1,z/y^k)$ is also a solution of …
11
votes
Accepted
Mordell-Weil of an elliptic surface after adjoining a nontorsion section: as small as possible?
I do not believe you have equality in general. I sketch a counterexample below, which is a geometric version of the fact that if $E/K$ is an elliptic curves such that the quadratic twist $E^{(d)}/K$ h …
5
votes
Mordell-Weil of an elliptic surface after adjoining a nontorsion section: as small as possible?
I will sketch a counterexample for the modified question. The idea behind the construction is similar to the counterexample for the original question. Only the geometric details of this construction a …
5
votes
Accepted
Selmer of an abelian variety versus that of its dual.
Let $\varphi:A\to A^t$ be a polarization. Then $\varphi$ is an isogeny.
In order to study the difference between the Selmer groups of $A$ and of $A^t$ you need to study the torsion subgroups of $A(K)$ …
3
votes
Polarizations of K3 surfaces over finite fields
Let $S$ be a smooth projective surface and $m:=\gcd(\deg \lambda)$ where $\lambda$ runs through the ample cone. Let $m'$ be the gcd of the entries of the intersection matrix of $S$
Then $m$ equals ei …
16
votes
Rank of $x (x^2 - 1) = c (c^2 - 1) y^2 $ over $\mathbb{Q}$ for given rational values of $c$
First you use $c$ as a parameter, i.e., consider your equation as elliptic curve over $\mathbb{Q}(c)$.
You can also consider this equation as an equation of an elliptic surface $S$. Now one easily pr …
9
votes
What heuristic evidence is there concerning the unboundedness or boundedness of Mordell-Weil...
I am not aware of much evidence for arbitrary high rank elliptic curves. Silverman in his book (Arithmetic of elliptic curves) gives as evidence the lack of evidence for the opposite statement. I gues …
4
votes
weight 4 eigenforms with rational coefficients---is it reasonable to expect they all come fr...
I am not that sure that your question can be answered positively, but the following is merely speculation, so you should not pin me down on it. The basic idea is that there might be "more" weight 4 fo …
10
votes
Does $(x^2 - 1)(y^2 - 1) = c z^4$ have a rational point, with z non-zero, for any given rati...
If you take the projective closure of your surface in $\mathbb{P}^3$ you find a singular quartic. This quartic has six singular points. Namely the two points found by Daniel and four points of the for …