 $\tau $-tilting theory
$\tau $-tilting theoryPublished online by Cambridge University Press: 03 December 2013
The aim of this paper is to introduce  $\tau $-tilting theory, which ‘completes’ (classical) tilting theory from the viewpoint of mutation. It is well known in tilting theory that an almost complete tilting module for any finite-dimensional algebra over a field
$\tau $-tilting theory, which ‘completes’ (classical) tilting theory from the viewpoint of mutation. It is well known in tilting theory that an almost complete tilting module for any finite-dimensional algebra over a field  $k$ is a direct summand of exactly one or two tilting modules. An important property in cluster-tilting theory is that an almost complete cluster-tilting object in a 2-CY triangulated category is a direct summand of exactly two cluster-tilting objects. Reformulated for path algebras
$k$ is a direct summand of exactly one or two tilting modules. An important property in cluster-tilting theory is that an almost complete cluster-tilting object in a 2-CY triangulated category is a direct summand of exactly two cluster-tilting objects. Reformulated for path algebras  $kQ$, this says that an almost complete support tilting module has exactly two complements. We generalize (support) tilting modules to what we call (support)
$kQ$, this says that an almost complete support tilting module has exactly two complements. We generalize (support) tilting modules to what we call (support)  $\tau $-tilting modules, and show that an almost complete support
$\tau $-tilting modules, and show that an almost complete support  $\tau $-tilting module has exactly two complements for any finite-dimensional algebra. For a finite-dimensional
$\tau $-tilting module has exactly two complements for any finite-dimensional algebra. For a finite-dimensional  $k$-algebra
$k$-algebra  $\Lambda $, we establish bijections between functorially finite torsion classes in
$\Lambda $, we establish bijections between functorially finite torsion classes in  $ \mathsf{mod} \hspace{0.167em} \Lambda $, support
$ \mathsf{mod} \hspace{0.167em} \Lambda $, support  $\tau $-tilting modules and two-term silting complexes in
$\tau $-tilting modules and two-term silting complexes in  ${ \mathsf{K} }^{\mathrm{b} } ( \mathsf{proj} \hspace{0.167em} \Lambda )$. Moreover, these objects correspond bijectively to cluster-tilting objects in
${ \mathsf{K} }^{\mathrm{b} } ( \mathsf{proj} \hspace{0.167em} \Lambda )$. Moreover, these objects correspond bijectively to cluster-tilting objects in  $ \mathcal{C} $ if
$ \mathcal{C} $ if  $\Lambda $ is a 2-CY tilted algebra associated with a 2-CY triangulated category
$\Lambda $ is a 2-CY tilted algebra associated with a 2-CY triangulated category  $ \mathcal{C} $. As an application, we show that the property of having two complements holds also for two-term silting complexes in
$ \mathcal{C} $. As an application, we show that the property of having two complements holds also for two-term silting complexes in  ${ \mathsf{K} }^{\mathrm{b} } ( \mathsf{proj} \hspace{0.167em} \Lambda )$.
${ \mathsf{K} }^{\mathrm{b} } ( \mathsf{proj} \hspace{0.167em} \Lambda )$.
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