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

3 votes
0 answers
154 views

Are these statements correct for all reductive groups, or just for $\operatorname{GL}_2$?

I'm reading the following notes on Brian Conrad's website. There are a couple of statements there which seem too good to be true. There is Proposition 3.6, which states: (Bernstein): Every irred …
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1 vote
0 answers
128 views

Is the root cone is contained in the weight cone?

Originally posted on math.stackexchange. Let $G$ be a semisimple algebraic group over a field $k$. Let $A_0$ be a maximal split torus of $G$, and $\mathfrak a_0 = \operatorname{Hom}(X(A_0), \mathbb …
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2 votes
0 answers
220 views

Classification of finite dimensional representations of split complex reductive groups

Finite dimensional, irreducible representations of simply connected, complex semisimple algebraic groups can be classified by their highest weight. I was wondering if there is an analogous classifica …
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3 votes
1 answer
76 views

Functions in the induced space compactly supported in $PN^-$ modulo $P$

Let $P_0$ be a minimal parabolic subgroup of a connected, reductive group $G$ over a $p$-adic field $k$. Let $P$ be a parabolic subgroup containing $P_0$ with Levi decomposition $P = MN$. Let $N^-$ …
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3 votes
0 answers
276 views

Errata for Casselman's unpublished notes

In the first chapter of W. Casselman's unpublished notes on representation theory, there is at least one stated result which is not true: A counterexample to this last result is given in the questi …
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2 votes
0 answers
47 views

If $f \in \operatorname{c-Ind}_Q^P \sigma$, then $f|_N$ is compactly supported modulo $Q \ca...

There is a claim in a proof in Casselman's notes on representation theory which I have not been able to verify. I have asked several people and nobody knows why it is true. The thing I can't figur …
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5 votes
1 answer
427 views

Generic supercuspidal representations of $\operatorname{GL}_n$ can be defined by integrals o...

Let $(V,\pi)$ be an irreducible, admissible, supercuspidal representation of $G = \operatorname{GL}_n(F)$ for $F$ a $p$-adic field. Let $B = TU$ be the usual Borel subgroup, maximal torus, and unipot …
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4 votes
0 answers
282 views

Meaning of a highly ramified character for reductive groups

Let $F$ be a $p$-adic local field, and $G$ a connected reductive group over $F$. What is the meaning of a "highly ramified character" of $G(F)$? I have seen this terminology in many places in repres …
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4 votes
0 answers
130 views

Supercuspidals and representations of $\operatorname{Gal}(\overline{F}/F)$

Let $F$ be a $p$-adic field, $G = \operatorname{Gal}(\overline{F}/F)$ and $W$ the Weil group of $F$. The inclusion map $W \subset G$ is continuous with dense image, so $\rho \mapsto \rho|_W$ defines …
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6 votes
1 answer
331 views

Irreducibility of the unramified principal series

Let $G = \operatorname{GL}_n(F)$ with the usual Borel subgroup $P = TU$. Let $\chi = \chi_1 \otimes \cdots \otimes \chi_n$ be an unramified character of $T$. Suppose that $\chi$ is regular, which is …
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13 votes
0 answers
397 views

Bernstein-Zelevinsky classification: viewing a representation as a subrepresentation or a qu...

$\DeclareMathOperator{\GL}{GL}$ $\DeclareMathOperator{\Ind}{Ind}$I have a question on the details of the Bernstein-Zelevinsky classification. This classification allows us to obtain irreducible repre …
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2 votes
2 answers
1k views

Definition of the weight lattice for a nonreduced root system

Let $(V,\Phi)$ be a root system with dual root system $(V^{\ast},\Phi^{\vee})$. Let $\Delta = \{\alpha_1, ... , \alpha_n\}$ be a set of simple roots for $V$, and let $\Delta^{\vee} = \{\alpha_1^{\vee …
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7 votes
1 answer
238 views

Definition of functions in the induced space from parabolic induction

Let $P$ be a parabolic subgroup of a connected, reductive group $G$ over a $p$-adic field. Let $M$ be a Levi subgroup of $P$, and let $N$ be the unipotent radical of $P$. If $(\pi,V)$ is a smooth, i …
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3 votes
1 answer
354 views

In a non-reduced root system, $s_{\alpha}(\beta)^{\vee} = s_{\alpha^{\vee}}(\beta^{\vee})$

In Bill Casselman's notes on root systems (http://www.math.ubc.ca/~cass/courses/tata-07a/Roots.pdf), I am confused about the proof of the result $s_{\alpha}(\beta)^{\vee} = s_{\alpha^{\vee}}(\beta^{\v …
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1 vote
0 answers
85 views

The convergence of the factor $\gamma(P)$ in the Iwasawa decomposition

Let $G$ be a connected, reductive group over a $p$-adic field $k$, $A_0$ a maximal split torus of $G$, and $P = MU$ a parabolic subgroup with $M$ containing $A_0$. Let $\overline{P} = M \overline{U}$ …
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