Cohomologie mod $p$ des fibr\'es en droites \'equivariants sur le demi-plan de Drinfeld

Abstract

We give a classification of all equivariant line of bundles on the semi-stable model $\hat{\mathbb{H}}$ of the Drinfeld upper half plane $\mathbb{H}$ on $\mathbb{Q}_p$ for a certain subgroup $[G]_2$ of ${\rm GL}_2(\mathbb{Q}_p)$ of index $2$. Then we study the cohomology groups of these line bundles that we restrict on the special fiber $\bar{\mathbb{H}}$ and this process provides a whole family of mod $p$ representations. In particular, we exhibit a class of $[G]_2$-equivariant line bundles on $\bar{\mathbb{H}}$ (the so-called positives of weight $-1$) and show that they are in one-to-one correspondence with the irreducible supersingular representations of $[G]_2$ (a notion we define) by taking the contragredient of the global sections.