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Finitistic dimensions and piecewise hereditary property of skew group algebras

Let $Λ$ be a finite dimensional algebra and $G$ be a finite group whose elements act on $Λ$ as algebra automorphisms. Under the assumption that $Λ$ has a complete set $E$ of primitive orthogonal idempotents, closed under the action of a Sylow $p$-subgroup $S \leqslant G$. If the action of $S$ on $E$ is free, we show that the skew group algebra $ΛG$ and $Λ$ have the same finitistic dimension, and have the same strong global dimension if the fixed algebra $Λ^S$ is a direct summand of the $Λ^S$-bimodule $Λ$. Using a homological characterization of piecewise hereditary algebras proved by Happel and Zacharia, we deduce a criterion for $ΛG$ to be piecewise hereditary.