The KD hypothesis for quotient-type pairs

Let (X,B)(X,B) and (Y,C)(Y,C) be pairs of quotient type with XX and YY projective. Let X~\widetilde X and Y~\widetilde Y be their associated smooth Deligne–Mumford stacks. Define KK-equivalence and the KK-inequality by requiring, on a common projective birational model ZZ, respectively f(KX+B)=g(KY+C)f^*(K_X+B)=g^*(K_Y+C) and f(KX+B)g(KY+C)f^*(K_X+B)\leq g^*(K_Y+C).

KD hypothesis. If (X,B)K(Y,C)(X,B)\sim_K(Y,C), then there is an equivalence

Φ:DbCoh(X~)DbCoh(Y~).\Phi:D^b\operatorname{Coh}(\widetilde X)\cong D^b\operatorname{Coh}(\widetilde Y).

If (X,B)K(Y,C)(X,B)\leq_K(Y,C), then there is a fully faithful functor

Φ:DbCoh(X~)DbCoh(Y~).\Phi:D^b\operatorname{Coh}(\widetilde X)\to D^b\operatorname{Coh}(\widetilde Y).

This extends the derived-category predictions from smooth varieties to quotient-type KLT pairs using associated smooth Deligne–Mumford stacks. The source presents it as a hypothesis and gives no resolution.

Sources & referencesView supporting material

Primary source

Yujiro Kawamata, “Birational geometry and derived categories”, arXiv:1710.07370 (2017).

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