ScalingStacks

Remark 2.10 . [048E]

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Remark 2.10.

The μ\mu-semistability condition can be recast in terms of the central charge Z⁡(E)=−d​e​g​(E)+−1​r​k​(E)Z(E)=-deg(E)+\sqrt{-1}rk(E), as saying arg⁡Z⁡(E′)≤arg⁡Z⁡(E)\arg Z(E^{\prime})\leq\arg Z(E) for all nonzero proper subsheaves E′⊂EE^{\prime}\subset E. It is worth emphasizing that except for the case of Riemann surfaces, μ\mu-stability does not give rise to a Bridgeland stability condition on Db​C​o​h​(X∨)D^{b}Coh(X^{\vee}), since skyscrapper sheaves will generally have zero rank and zero degree, hence zero central charge. A similar but more subtle failure of Bridgeland stability happens in the context of the deformed Hermitian-Yang-Mills connections (cf. [18, section 4]). Such a failure does not spell doom for the PDE applications, nor for DT theoretic applications.2424 24 R. Thomas defined DT invariants for μ\mu-stability long before the insight of Bridgeland. Even though Bridgeland stability seems to be a plausible framework for special Lagrangians in the light of Joyce’s proposal, it is probably advisable to maintain a more flexible attitude to stability conditions.

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