Specht Modules With Trivial Direct Summands

Abstract

We prove that, in characteristic $2$, a Specht module indexed by a nonhook partition cannot have a trivial direct summand. The proof uses the KLR grading and a recent graded homomorphism theorem of Hudak. Together with Murphy's theorem for hooks, this gives the complete classification of trivial direct summands of Specht modules in characteristic $2$, answering a question posed by Collins--Dodge and Dodge--Van Vlack.