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4 votes
1 answer
261 views

Local triviality of Galois cohomology classes over $\mathbb{Q}$

Let $A$ be a $\mathrm{Gal}(\bar{\mathbb{Q}}/\mathbb{Q})$-module which is a finitely generated free $\mathbb{Z}$-module. I'm interested in the behaviour of cohomology classes in $$\mathrm{H}^1(\mathbb …
Daniel Loughran's user avatar
4 votes
0 answers
123 views

Unramified Galois cohomology

Let $k$ be a local field with absolute Galois group $\Gamma_k$, inertia subgroup $I_k \subset \Gamma_k$, and residue field $\mathbb{F}$. Let $M$ be a finite Galois module over $k$. The unramified Galo …
Daniel Loughran's user avatar
11 votes

Which groups are Galois over some p-adic field?

I'll upgrade my comment to an answer. Any finite Galois extension of $\mathbb{Q}_l$ of degree coprime to $l$ is tamely ramified. In particular, its Galois group is an extension of two cyclic groups. …
Daniel Loughran's user avatar
9 votes
1 answer
606 views

Characters of simply connected semsimple algebraic groups over local fields

Let $G$ be a semisimple algebraic group over $\mathbb{Q}_p$. Then by definition $G$ admits no non-trivial algebraic characters, i.e. homomorphisms $G \to \mathbb{G}_m$. However, it is quite possible …
Daniel Loughran's user avatar
3 votes
Accepted

Understanding the structure of unitary groups

As you already seem to know, unitary groups are classified by separable quadratic field extensions (in fact one should really work with separable quadratic algebras, i.e. also $F\times F$, correspondi …
Daniel Loughran's user avatar