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Linear representations of algebras and groups, Lie theory, associative algebras, multilinear algebra.

7 votes
2 answers
418 views

Separating subspaces in an irreducible representation

Suppose $G$ is a semisimple $\mathbb{R}$-algebraic group with finite center, and suppose $G$ acts irreducibly on a vector space $V$. Suppose $U \subset V$ and $W \subset V$ are subspaces. $\mathbf{Q …
Alex Eskin's user avatar
  • 3,201
23 votes

What invariants of a matrix or representation can be used to find its GL(n,Z)-conjugacy class?

In each conjugacy class you can always find a representative which is block upper triangular, and the diagonal blocks have irreducible characteristic polynomials. This gives a partial reduction to the …
Alex Eskin's user avatar
  • 3,201
9 votes

Are there some nontrivial group homomorphisms from $SL_n(\mathbb{Z})$ to $GL_{n-1}(\mathbb{Z...

By the Margulis superrigidity theorem, any homomorphism from $SL(n,\mathbb{Z})$ to $SL(n-1,\mathbb{R})$ with infinite image has to extend to a homomorphism from $SL(n,\mathbb{R})$ to $SL(n-1,\mathbb{R …
Alex Eskin's user avatar
  • 3,201
13 votes
Accepted

Lattices in $SL(n,\mathbb R)$

The answer is yes. It is theorem [2.13] of the following paper of Prasad and Raghunathan: Prasad, Gopal; Raghunathan, M. S. Cartan subgroups and lattices in semi-simple groups. Ann. of Math. (2) 96 ( …
Alex Eskin's user avatar
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