bio | website | stankewicz.net |
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location | ||
age | ||
visits | member for | 5 years |
seen | Jan 25 at 14:22 | |
stats | profile views | 1,360 |
Postdoc at the University of Bristol
Jan 19 |
awarded | Yearling |
Nov 6 |
awarded | Popular Question |
Nov 6 |
awarded | Necromancer |
Sep 24 |
awarded | Autobiographer |
Jun 5 |
comment |
A pointless circle in HoTT
What is your definition of "inhabited by"? |
Jun 4 |
comment |
Source of quotation about the waste-baskets of physicists
Well to have been more accurately (R.I.P.) |
May 5 |
comment |
Is GL2( R ) - > PGL2( R ) surjective?
In general the map will be surjective when Pic(R) is trivial. Brian Conrad's homework on group schemes walks you through this to a certain extent. If R as a Dedekind domain you can think of the elements of $PGL_n(R)$ as being pseudomatrices of fractional ideals all of whose $n$-fold products which go into the determinant are principal. If the class group is trivial, then all the entries have to be principal anyway and you're left with a standard matrix in $GL_n(R)$ up to unit multiple in $R$. |
Apr 24 |
comment |
Spicing up Riemann surfaces course (revised)
What's so bland about Riemann Surfaces that requires spicing up? |
Apr 12 |
answered | Quadratic twist of an elliptic curve given by non-Weierstrass model |
Apr 10 |
comment |
Canonical lifts from $\mathbb F_q$ and CM-theory
I have two references in mind: 1) Messing's book shows how if $A_{/k}$ is an ordinary abelian variety then the Serre-Tate Canonical lift $\mathcal{A}_{W(k)}$ admits an isomorphism $End_k(A) \cong End_{W(k)}(\mathcal{A})$. 2) Deligne's Inventiones paper "Varieties Abeliennes Ordinaires..." shows how the choice of embedding $W(k) \hookrightarrow \mathbf{C}$ doesn't change anything. He therefore shows an equivalence of categories between ordinary abelian varieties over a finite field vs $\mathbf{C}$ whose details escape me at the moment but the paper is 3 pages so you should read it anyway :) |
Apr 1 |
comment |
Etale covers of a hyperelliptic curve
You're right. I still think there's a way to say that if $Y$ was also Galois then there's a way to break it up into a composite cover with $X$ in the middle but I don't really have any evidence for that. |
Apr 1 |
revised |
Etale covers of a hyperelliptic curve
edit: removed previous edit |
Apr 1 |
revised |
Etale covers of a hyperelliptic curve
added 273 characters in body |
Apr 1 |
answered | Etale covers of a hyperelliptic curve |
Mar 12 |
comment |
Connections between Riemann hypothesis for curves over finite fields and Ramanujan property for graphs
For Ramanujan graphs coming Cayley graphs I don't know the exact story, but using Brandt matrices you can get Ramanujan graphs out of the dual graphs of certain Shimura curves. Pete Clark has some "rambling notes" on this subject here math.uga.edu/~pete/ramanujanrevisited.pdf and I covered some smaller cases in a course I taught a year ago. |
Jan 27 |
awarded | Necromancer |
Jan 19 |
awarded | Yearling |
Dec 20 |
awarded | Revival |
Dec 17 |
comment |
divisibility of Tamagawa numbers
Thank you, that was very silly of me. Explicitly, Reichert's paper on torsion structures over quadratic fields gives an example with p= 13. |
Dec 17 |
comment |
divisibility of Tamagawa numbers
A number of people commented that there is a counterexample for $p=5$, which is of course not quite what you're asking about. I'll just note that the Tamagawa number of an elliptic curve over a dvf is essentially the valuation of the minimal discriminant (and thus $\le 12$) if it has split multiplicative reduction and something else (not a large prime) otherwise. So we're really talking about $p=11$ on the nose here and having sage search through (some fraction of) the Cremona database didn't find anything with tamagawa number divisible by 11. |