Derived equivalence of algebras induced by their trivial extensions

Abstract: The bounded derived category of a finite dimensional algebra of finite global dimension is equivalent the stable category of $\mathbb{Z}$-graded modules over its trivial extension \cite{Happel}. In particular, given two derived equivalent finite dimensional algebras $\Lambda_{1}$ and $\Lambda_{2}$ of finite global dimension, their trivial extensions are stable equivalent. The converse is not true in general. The goal of this paper is to study cases where derived equivalences between $\Lambda_{1}$ and $\Lambda_{2}$ arise from an equivalence of categories involving their trivial extension. Thanks to a graded version of Happel's theorem, we show that one can construct a $\mathbb{Z}$-grading on the $\Lambda_{i}$ so that such an equivalence involving their trivial extension yield a derived equivalence between the category of $\mathbb{Z}$-graded module over $\Lambda_{i}$. We describe explicitly the tilting object associated to this derived equivalence (in the non-graded and in the graded case) for triangular matrix algebras. Finally, we apply these results to the particular case of gentle algebras. In this context, we study how one can obtain a derived equivalence between $\Lambda_{1}$ and $\Lambda_{2}$ (in the non-graded and the graded case) from graded generalized Kauer moves.