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arxiv: 1806.07780 · v2 · pith:OC2YRR7Rnew · submitted 2018-06-20 · 🧮 math.RT

Calculations with graded perverse-coherent sheaves

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keywords characteristicmathbbmathrmsheavesgradedgrouppartperverse-coherent
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In this paper, we carry out several computations involving graded (or $\mathbb{G}_{\mathrm{m}}$-equivariant) perverse-coherent sheaves on the nilpotent cone of a reductive group in good characteristic. In the first part of the paper, we compute the weight of the $\mathbb{G}_{\mathrm{m}}$-action on certain normalized (or "canonical") simple objects, confirming an old prediction of Ostrik. In the second part of the paper, we explicitly describe all simple perverse coherent sheaves for $G = PGL_3$, in every characteristic other than 2 or 3. Applications include an explicit description of the cohomology of tilting modules for the corresponding quantum group, as well as a proof that $\mathsf{PCoh}^{\mathbb{G}_{\mathrm{m}}}(\mathcal{N})$ never admits a positive grading when the characteristic of the field is greater than 3.

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