4,914 reputation
11835
bio website perso.ens-lyon.fr/…
location Lyon, France
age 38
visits member for 5 years, 2 months
seen 2 days ago
I am a number theorist working in Lyon (France).

Apr
8
comment Algebraic integer with conjugates on the unit circle
The same is true of $\alpha^k$ and the characteristic polynomials of the $\alpha^k$ have coeffts that are bounded indept of $k$. A lot of them must be equal to each other, so $\alpha^k = \alpha^\ell$ for some $k$ and $\ell$.
Mar
1
comment Can an abelian variety/Q have no non-trivial points over Q_sol?
@Pablo sorry, my mistake!
Mar
1
comment Can an abelian variety/Q have no non-trivial points over Q_sol?
By definition, an abelian variety over a field K has a rational point over K, so in your question, you presumably mean a homogenous space for your abelian variety.
Jan
27
comment Number of common solutions of polynomial system
See for instance the introduction to arxiv.org/abs/1408.3224
Jul
26
comment Linear map with two “incompatible” representations
Very nice, thank you!
Jul
24
comment 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
comment is there a p-adic implicit function theorem?
See page 73 of the latest edition of Serre's book.
Jul
13
comment 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
comment 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
comment 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
comment 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
comment Status of local Langlands conjecture over positive characteristic
Laumon pas Laumont!
Nov
26
comment 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
comment De Rham cohomology of formal groups
@Jon Beardsley: thank you!
Oct
1
comment $(\varphi, \Gamma)$-modules of finite height
"Since representations that aren't of finite height do exist": take a semistable noncrystalline representation.
Sep
10
comment 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
comment $(\varphi, \Gamma)$-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
comment Cyclotomic extension of p-adic fields
Oh ok, thank you for the clarification!
Jul
9
comment 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
comment 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.