an:00665866
Zbl 0835.14019
Schwarz, Gerald W.
Differential operators on quotients of simple groups
EN
J. Algebra 169, No. 1, 248-273 (1994).
00022287
1994
j
14M17 16S32 13N10 14L30
algebraic group acting on a complex algebraic variety; algebra of algebraic differential operators; quotient morphism
Let \(X\) be an affine complex algebraic variety, and let \(\Delta (X)\) denote the (non-commutative) algebra of algebraic differential operators on \(X\). Then \(\Delta (X)\) has a filtration \(\{\Delta^n (X)\}\) by order of differentiation, and the associated graded algebra \(\text{gr} \Delta (X)\) is commutative. Let \(X\) be smooth and a \(G\)-variety \((G\) is a reductive complex algebraic group). Let \(\pi_X : X \to X/G\) be the quotient morphism. Then one has a natural map \((\pi_X)_* : (\Delta^n (X))^G \to \Delta^n (X/G)\). The main aim of the paper is the following:
Theorem. Let \(G\) be simple and connected, and let \(V\) be an irreducible nontrivial \(G\)-module such that \(\dim V/G > 0\). Then the following are equivalent
(1) \(V\) is 2-modular;
(2) \(V\) is 2-large;
(3) \((\pi_V)_*\) is graded surjective;
(4) \((\pi_V)_*\) is surjective;
(5) \(V/G\) has no codimension one strata;
(6) \(V\) is not coregular.
R.Salvi (Milano)