4
votes

Accepted

### Intuition for Luna's Étale Slice Theorem

Luna Étale's Slice Theorem is probably the most powerful result we have to understand the local structure of a moduli space.
Moduli spaces (say of semi-stable vector bundles on a smooth projective ...

- 6,533

3
votes

### Structure of cuspidal Bernstein components—do non-commutative endomorphism rings ever really show up?

A lot of time has passed, so perhaps this question is moot for you [I mean, I saw you give the Plücker lectures last week on something very different],
or perhaps you now know the answer. But since ...

- 403

1
vote

### Schur multiplier of $\mathrm{SL}(2,\mathbb{Q})$

$\DeclareMathOperator\SL{SL}\DeclareMathOperator\Sp{Sp}$For a field $F$, the group $H_2(\SL_2(F))$ has a presentation in terms of the symplectic Steinberg symbols. This is shown in Matsumoto's paper [...

- 329

1
vote

Accepted

### A result of Borel on extensions of arithmetic groups

A proof appears in Section 2.3 of my paper Mapping class groups of manifolds with boundary are of finite type. As pointed out in the comments, it is crucial that $G$ is unipotent.

- 7,658

Only top scored, non community-wiki answers of a minimum length are eligible

#### Related Tags

algebraic-groups × 1945ag.algebraic-geometry × 827

rt.representation-theory × 457

gr.group-theory × 319

lie-groups × 314

reference-request × 184

reductive-groups × 160

lie-algebras × 157

nt.number-theory × 139

finite-groups × 85

linear-algebra × 59

automorphic-forms × 50

arithmetic-geometry × 47

group-schemes × 47

algebraic-number-theory × 45

root-systems × 45

invariant-theory × 43

galois-cohomology × 41

ac.commutative-algebra × 40

arithmetic-groups × 39

p-adic-groups × 38

group-actions × 37

geometric-invariant-theory × 34

matrices × 29

weyl-group × 29