bio  website  mathematik.unimainz.de/… 

location  Mainz  
age  27  
visits  member for  5 years, 1 month 
seen  3 hours ago  
stats  profile views  2,742 
Postdoc at JohannesGutenberg Universität Mainz. Interested in many things, but especially arithmetic geometry.
3h

comment 
When does an algebraic space that is a torsor over a scheme have to be a scheme?
Check out arxiv.org/abs/1501.04304 . 
Mar 24 
revised 
Abelian varieties with good reduction everywhere over function fields
edited tags 
Mar 24 
answered  Abelian varieties with good reduction everywhere over function fields 
Mar 22 
comment 
$\mathcal{M}_{g,n}$ a scheme for $n \gg 0$?
@TimoKeller To answer your question in the comments of the other question, see Corollary 8.1.1 in the book Champs Algebriques by Laumon and MoretBailly: Any DM stack with trivial stabilizers is an alg space. To see that an alg space is a scheme you can apply Knudson's criterion sometimes and use properties of the coarse moduli space as S. Carnahan mentions. (For Knudson's criterion see Cor. II.6.16 of his book on Alg Spaces.) 
Mar 2 
awarded  Yearling 
Feb 18 
comment 
Automorphisms of generic complete intersections
...the problem therefore becomes showing the analogue of 2). Namely, showing the injectivity of the canonical map $Aut(X) \to Aut(H^n_{prim}(X)$ (which is easy in fact if $\sum d_i > n+1$). As you note, 1) and 2) only show that the generic autom group is then trivial or $\mathbb Z/2\mathbb Z$. To exclude that there are autom's acting as $1$ on cohomology (ie. prove 3) might be a bit difficult because as you say the (highly singular) quotient will be a fake projective space. The only way to do this I know of is using Lefschetz trace formula. 
Feb 18 
comment 
Automorphisms of generic complete intersections
The argument you have in mind (I think) also appears in the book of KatzSarnak when they show that the generic autom group of a smooth curve of genus $g>1$ is trivial. They do this by combining 1) the bigness of the monodromy group with 2) the injectivity of the map $Aut(X) \to Aut(H^1(X))$ and 3) the fact that a generic curve $X$ is not hyperelliptic (so that no automorphism of $X$ induces $1$ on $H^1$). In the case of complete intersections, the bigness still holds (see the book by PetersSteenbrink for a reference).... 
Feb 17 
revised 
MumfordTate groups of products of Hodge structures
Fixed a small typo 
Feb 2 
revised 
What implications would a solution of the *Standard Conjectures* have on the *Hodge Conjecture*?
added 1 character in body 
Jan 19 
answered  there exists a hypersurface H ⊂ X such that X \ H is Stein and L is trivial over X \ H 
Jan 15 
reviewed  Approve The Metrizability of Symmetric Products of Metric Spaces 
Jan 14 
revised 
Isotriviality: two definitions
deleted 1 character in body 
Jan 14 
answered  Isotriviality: two definitions 
Dec 29 
comment 
sanity check about a morphism from a stack to its coarse moduli space
@TomGraber Thank you for your comment. I think User74230 meant to write "quasifinite" instead of "etale". This makes me wonder: aren't all etale morphisms representable? 
Dec 25 
answered  sanity check about a morphism from a stack to its coarse moduli space 
Dec 21 
comment 
An extension of group schemes admitting Neron models
On the other hand, the implications a implies b and a implies e of Thm 10.2.1 hold in general (as you probably already know). There might be a way to circumvent the compactification results and to prove that a group scheme not containing any copy of G_a or G_m is "bounded" directly (but I doubt it...). 
Dec 21 
comment 
An extension of group schemes admitting Neron models
If I'm not mistaken, the necessary "compactification" resuts used in Thm 10.2.1 are now known for not necessarily commutative group schemes by the work of Gabber. Try googling Gabber's compactification theorem to see if you get something useful. 
Dec 21 
reviewed  Reject Refereeing a Paper 
Dec 20 
answered  Is there a Riemann existence theorem for orbifolds? 
Dec 19 
revised 
Weil height of an Abelian Variety with everywhere (potentially) good reduction
deleted 1 character in body 