Copyright © The Author 2007. Published by Oxford University Press.
An Extension of James's Conjecture
Queen Mary, University of London, Mile End Road, London E1 4NS, U.K.
Correspondence: Correspondence to be sent to: m.fayers{at}qmul.ac.uk
Let B be a block of an IwahoriHecke algebra or q-Schur algebra of the symmetric group. The decomposition matrix for B may be obtained from the decomposition matrix of the corresponding block B' in infinite characteristic by post-multiplying by an adjustment matrix; since (by a deep theorem of Ariki) there is an algorithm for computing the decomposition matrix for B', the hard part of the decomposition number problem for B is to find the adjustment matrix. James's Conjecture suggests a sufficient condition for this adjustment matrix to be the identity matrix. We extend James's Conjecture to give a necessary and sufficient condition, and prove the necessity of our condition.