Stability conditions, torsion theories and tilting

The space of stability conditions on a triangulated category is naturally partitioned into subsets U() of stability conditions with a given heart . If has finite length and n simple objects then U() has a simple geometry, depending only on n. Furthermore, Bridgeland has shown that if ℬ is obtained from by a simple tilt, that is, by tilting at a torsion theory generated by one simple object, then the intersection of the closures of U() and U(ℬ) has codimension 1. Suppose that , and any heart obtained from it by a finite sequence of (left or right) tilts at simple objects, has finite length and finitely many indecomposable objects. Then we show that the closures of U() and U(ℬ) intersect if and only if and ℬ are related by a tilt, and that the dimension of the intersection can be determined from the torsion theory. In this situation the union of subsets U(ℬ), where ℬ is obtained from by a finite sequence of simple tilts, forms a component of the space of stability conditions. We illustrate this by computing (a component of) the space of stability conditions on the constructible derived category of the complex projective line stratified by a point and its complement.