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The Hall algebra of a cyclic quiver and canonical bases of Fock spaces
We show that the Ringel-Hall algebra
of the cyclic quiver of type
is equal to the tensor product of the (negative nilpotent) quantized enveloping algebra
with a polynomial algebra
. We use this to prove the conjecture of Varagnolo and Vasserot relating the "geometric" canonical basis of the level-1 Fock space (defined via the action of the Hall algebra) with the Leclerc-Thibon basis. In particular, this completes the approach by Varagnolo and Vasserot to a q-analogue of the Lusztig character formula for simple modules over quantum
at roots of unity. Finally, we generalize the previous results to the higher level Fock spaces defined by Uglov.