bio | website | perso.ens-lyon.fr/… |
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location | Lyon, France | |
age | 37 | |
visits | member for | 4 years, 6 months |
seen | Oct 14 at 15:39 | |
stats | profile views | 2,945 |
I am a number theorist working in Lyon (France).
Jul 26 |
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Linear map with two “incompatible” representations
Very nice, thank you! |
Jul 24 |
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If $G$ is compact, $H \leq G$ open, $V$ an irreducible $H$-rep, is $\text{Ind}_H^G$ semisimple?
The continuity of the action does not imply that V is finite diml. |
Jul 13 |
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is there a p-adic implicit function theorem?
See page 73 of the latest edition of Serre's book. |
Jul 13 |
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Power series defined by Witt vectors / Teichmüller representatives of p-adics
... "Quiconque s’est intéressé aux corps locaux sait bien qu’une extension très ramifiée du corps $Q_p$ des nombres $p$-adiques ressemble à s’y méprendre à un corps de séries formelles à coefficients dans son corps résiduel. C’est sans doute Marc Krasner qui a tenté le premier de formuler ce phénomène abondamment utilisé depuis en théorie de Hodge p-adique [...]" (Fontaine, Bourbaki 1057). |
Jul 13 |
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Power series defined by Witt vectors / Teichmüller representatives of p-adics
If you take $K$ to be ramified and play the same game, then as you increase the ramification, your two fields are "more and more isomorphic". This observation of Krasner is the basis for the theory of the "field of norms" and more recently the theory of "perfectoid spaces". Here is what Fontaine says about this in his recent Bourbaki exposé... |
Jul 13 |
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What is the lowest-weight non-cyclotomic Galois representation in $\overline{\mathcal M}_{g,n}$?
I think that Gaëtan Chenevier is thinking about these things as well, you could ask him directly. |
May 2 |
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How to correct an error in a submitted paper?
Same here - I recently had a paper rejected on the basis of three reports, one of which was a very angry report which was not based on the version of the paper that I'd sent to the journal. My paper, however, stayed rejected after this was pointed out :-( |
Feb 6 |
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Status of local Langlands conjecture over positive characteristic
Laumon pas Laumont! |
Nov 26 |
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maximal abelian extension of quadratic extension of $\mathbb Q_p$
You can always take $f(T)=\pi T + T^q$ where $\pi$ is a uniformizer and $q$ is the cardinality of the residue field. Any power series satisfying the conditions that you wrote will do. |
Oct 16 |
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De Rham cohomology of formal groups
@Jon Beardsley: thank you! |
Oct 1 |
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$(\varphi, \Gamma)$-modules of finite height
"Since representations that aren't of finite height do exist": take a semistable noncrystalline representation. |
Sep 10 |
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Why does $H^i(X_{ét},\mathbb{Q}_p)$ have a Hodge-Tate structure?
As Keerthi pointed out, it's after you tensor by Cp that the powers of the cyclo char appear. But a statement like that is true for any Galois repn V by Sen's theory. What is specific to the étale cohomology is that it's integer powers of the cyclo char that appear. This is where you use the geometric input. As to why this is so... |
Aug 27 |
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$(\varphi, \Gamma)$-module of dimension 2 modulo $p$
"Finite height" does mean that in some basis, there are no denominators. This does not imply the same property holds in your favorite basis :) |
Jul 9 |
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Cyclotomic extension of p-adic fields
Oh ok, thank you for the clarification! |
Jul 9 |
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Cyclotomic extension of p-adic fields
@Larsson: "Typical"? :-( See math.u-psud.fr/~biblio/pub/2000/abs/ppo2000_24.html for the preprint version of Fontaine's paper, and see mathoverflow.net/questions/96257/… concerning the availability of Asterisque. |
Jul 8 |
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Cyclotomic extension of p-adic fields
What do you mean "what can be said"? If you add the $p^n$-th roots of $1$ for all $n$, (and not just the $p$-th roots as in your question) you get an extension whose Galois group is an open subgroup of $Z_p^\times$, and whose residue field is a finite extension of $F_p$. These extensions are used a lot in $p$-adic Hodge theory, so I suggest you look at papers in that area, eg Fontaine's "Arithmétique des représentations galoisiennes $p$-adiques". There's a lot of info about the ramification of that extension, for example. |
Jul 5 |
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Does there exist a non-square number which is the quadratic residue of every prime?
On the other hand, 16 is an 8th power modulo every prime! |
Jul 4 |
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Omitting primes from a Hecke algebra
@Kevin: "So knowing a Galois representation mod 2 does not tell you what the crystalline Frobenius eigenvalues are mod 2". I'm not sure exactly what you mean, but if ell=p, then the mod p Galois repn carries very little information about the Galois repn and the crystalline Frobenius. |
Jun 24 |
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Is there a known example of a curve X of genus > 1 over Q such that we know the number of points of X over the n-th cyclotomic field, for every n?
Concerning solvable points on projective curves: there are some results of Ciperiani and Wiles "Solvable points on genus one curves" and of Pal as well "Solvable points on projective algebraic curves", "Solvable points on genus one curves over local fields" and "Curves which do not become semi-stable after any solvable extension". |
Jun 7 |
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Roadmap to reach Arithmetic Geometry for a Physics Major
Take a look at the book "From Number Theory to Physics". Exerpt from the blurb : "The 14 chapters of this book are extended, self-contained versions of expository lecture courses given at a school on "Number Theory and Physics" held at Les Houches for mathematicians and physicists. Most go as far as recent developments in the field. Some adapt an original pedagogical viewpoint." |