Un scindage du morphisme de Frobenius quantique

Abstract

We show that the quantum Frobenius morphism constructed by Lusztig in the setting of the quantum enveloping algebra specialized at a root of unity admits a multiplicative splitting (non unital). We also find a basis of the toral part of the small quantum algebra consisting of pairwise orthogonal idempotents summing up to 1, and likewise in the modular case of the algebra of distributions for a semisimple algebraic group.

Thanks to enlightning comments of Prof. Yoshihisa Saito on v.1, the proof of thm. 1.5 has been simplified with misprints/Inacuracies corrected

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