Published online by Cambridge University Press: 02 October 2015
Let $G$ be a reductive algebraic group over an algebraically closed field of positive characteristic,
$G_{1}$ the Frobenius kernel of
$G$, and
$T$ a maximal torus of
$G$. We show that the parabolically induced
$G_{1}T$-Verma modules of singular highest weights are all rigid, determine their Loewy length, and describe their Loewy structure using the periodic Kazhdan–Lusztig
$P$- and
$Q$-polynomials. We assume that the characteristic of the field is sufficiently large that, in particular, Lusztig’s conjecture for the irreducible
$G_{1}T$-characters holds.