5,368 reputation
21439
bio website iazd.uni-hannover.de/…
location Hanover, Germany
age 30
visits member for 5 years, 4 months
seen 6 hours ago

I am a postdoc at the Leibniz Universität Hannover. I specialise in arithmetic geometry, algebraic number theory and analytic number theory.


Jul
25
asked Finite-index subgroups of the ideles
Jun
26
comment References for modular curves over finite fields
I'm voting to close this question as off-topic because this was answered on math.stackexchange.
Jun
25
accepted Specialisation of rigid varieties
Jun
25
comment Specialisation of rigid varieties
Ok. If you know of any counter-examples in the Fano case, I would be most interested.
Jun
25
comment Specialisation of rigid varieties
Is the Mukai-Umemura threefold really rigid? I thought that prime Fano threefolds of genus 12 had positive dimensional moduli.
Jun
25
comment Specialisation of rigid varieties
Hi Jason. Thanks for the answer! Your examples seem to suggest that things are a lot better behaved in the Fano case. Do you know of any counter-examples to my question if I moreover assume that the special fibre and generic fibre are both Fano?
Jun
25
asked Specialisation of rigid varieties
Jun
20
answered meaning of $k$-rational for closed subschemes
Jun
17
comment Number of solutions in a sum of squares Diophantine equation
I'm voting to close this question as off-topic because it has been answered.
Jun
15
accepted Non-algebraic K3 surfaces in characteristic $p$
Jun
15
comment Non-algebraic K3 surfaces in characteristic $p$
Quite possibly; does every non-algebraic K3 surface over $\mathbb{C}$ arise this way?
Jun
15
asked Non-algebraic K3 surfaces in characteristic $p$
Jun
8
accepted Picard groups of Fano varieties in positive characteristic
Jun
4
comment Picard groups of Fano varieties in positive characteristic
@Jason: I don't quite follow, what is the problem with small $\ell$? Is the issue with possible $\ell^\infty$-torsion in the Brauer group? Won't this problem "go away" as we are taking a projective limit over all $\mathrm{Br}[\ell^n]$?
Jun
3
comment Picard groups of Fano varieties in positive characteristic
Thanks for the answer Jason. I will have a think about the argument you give. Do you know a precise reference where finiteness of the Brauer group of rationally connected varieties is proved?
Jun
3
asked Picard groups of Fano varieties in positive characteristic
Jun
1
comment Isotropic ternary forms
Use stereographic projection.
May
31
comment Are there infinitely many N^3 (especially for prime N) that cannot be expressed as a sum of three positive cubes?
Also, as you no doubt know, determining which integers are a sum of three (possibly negative) cubes is a very difficult open problem (see e.g. mathoverflow.net/questions/138886/…). One would think that your problem were easier as you are working with a cube, but restricting to positive cubes seems to complicate things.
May
31
comment Are there infinitely many N^3 (especially for prime N) that cannot be expressed as a sum of three positive cubes?
This problem seems quite difficult. The issue, of course, is that there are no local obstructions in this case: there are always solutions in all $\mathbb{Z}_p$ and $\mathbb{R}$. So you would need to try to use a finer obstruction, e.g. a Brauer-Manin obstruction.
May
27
comment Obstruction to get a galois invariant cycle
Actually the Tate conjecture only applies with rational coefficients whereas here you are working with integral coefficients, so it perhaps not so clear whether the Tate conjecture can be used.