Let $R$ be a commutative ring If $\mathcal{ C}_1$ and $\mathcal{ C}_2$ are $R$-linear triangulated categories then we can give an obvious triangulated structure on $\mathcal{ C} = \mathcal{ C}_1 \oplus \mathcal{ C}_2$ where $Hom_\mathcal{ C}(U, V) = 0$ if $U \in \mathcal{ C}_i$ and $V \in \mathcal{ C}_j$ with $i \neq j$. We say a $R$-linear triangulated category $\mathcal{ C}$ is disconnected if $\mathcal{ C} = \mathcal{ C}_1 \oplus \mathcal{ C}_2$ where $\mathcal{ C}_i$ are non-zero triangulated subcategories of $\mathcal{ C}$. Let $\mathcal{ C}_i$ and $\mathcal{ D}_j$ be connected triangulated $R$ categories with $i \in \Gamma$ and $j \in \Lambda$. Suppose there is an equivalence of triangulated $R$-categories \[ \Phi \colon \bigoplus_{ i \in \Gamma}\mathcal{ C}_i \xrightarrow{ \cong} \bigoplus_{ j \in \Lambda}\mathcal{ D}_j \] Then we show that there is a bijective function $\pi \colon \Gamma \rightarrow \Lambda$ such that we have an equivalence $\mathcal{ C}_i \cong \mathcal{ D}_{ \pi(i)} $ for all $i \in \Gamma$. We give several examples of connected triangulated categories and also of triangulated subcategories which decompose into utmost finitely many components.
Categories: math.AC math.AG math.RT