Some methods of computing first extensions between modules of graded Hecke algebras

Abstract

In this paper, we establish connections between the first extensions of simple modules and certain filtrations of of standard modules in the setting of graded Hecke algebras. The filtrations involved are radical filtrations and Jantzen filtrations. Our approach involves the use of information from the Langlands classification as well as some deeper understanding on some structure of some modules. Such module arises from the image of a Knapp-Stein type intertwining operator and is a quotient of a generalized standard module. Along the way, we also deduce some results on the blocks for finite-dimensional modules of graded Hecke alebras. As an application, we compute the Ext-groups for irreducible modules in a block for the graded Hecke algebra of type $C_3$, assuming the truth of a version of Jantzen conjecture.