MAST90017 Representation theory 2023 Semester 2 Assignment 2
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
MAST90017 Representation theory
2023 Semester 2
Assignment 2
Due by 11 am on Oct 20 (Friday) in class
(1) Let k be a inite ield and let
Let Let ω be a homomorphism of k* = k 一 {0} into C* .
Consider the degree 1 representation ϕω of H deined by
Use Mackey’s irreducibility criterion to show that the representation IndH(G) ϕω of G induced by ϕω is irreducible if and only if ω2 1.
(2) Let G be the group of permutations of {1, 2, 3, 4}. Let A be the subset of G consisting of the trivial permutation and the three permutations (12)(34) , (13)(24), (14)(23). Here (ij) denotes a transposition interchanging i,j.
(a) Show that A is a normal subgroup of G.
(b) Let H be the subgroup of G consisting of permutations which keep 4 ixed. Show that G is a semidirect product of A and H.
(c) Using the description of the irreducible representations of a semidirect product we discussed in class, determine the degrees of irreducible representations of G over C, and construct an irreducible representation that is isomorphic to the standard representation V = {(x1 , x2 , x3 , x4 ) ∈ C4 | x1 + x2 + x3 + x4 = 0} of G.
(3) Let Fq be a initeield with q elements, where q = pn for some prime p. Let G be the group of transformations,
Fq → Fq : x →7 ax + b, a ∈ Fq(*), b ∈ Fq .
Find all irreducible representations of G over C, and compute their characters.
(4) Let C =:i<j (ij) 2 C[Sn] be the sum of all transpositions in the symmetric group Sn.
Let V = C[Sn]c be the irreducible representation of Sn corresponding to the parti- tion λ of n, where λ = (λ1 , λ2 , · · · , λk ), λi ≥ λi+1 > 0, i = 1, . . . , k — 1.
(a) Show that C acts on V by multiplication by a scalar.
(b) Show that the scalar in (a) equals mP — mQ =:j :i1 (i — j), where mP (resp. mQ ) denotes the number of transpositions in the Young subgroup P (resp. Q ).
(5) Let A be the Weyl algebra k〈x, y)/〈yx — xy — 1), where k is an algebraically closed ield.
(a) Suppose that chark = 0. Find all inite dimensional representations of A.
(b) Suppose that chark = p > 0. Show that xp , yp 2 Z(A) = fa 2 A j ab = ba for all b 2 Ag, the center of the algebra A. Find all inite dimensional irre- ducible representations of A.
2023-10-19