Saturday, 1 March 2008

ag.algebraic geometry - Graded or stacky Serre duality

Theres graded local duality which works just like local duality; however, it requires that A0 is a field. I've had some luck making things work when A_0 is not a field, but then the local duality becomes more derived. Specifically, Matlis duality, which is an exact functor in the graded local case, gets replaced by operatornameRHomA0(,A0), the derived graded hom over A0 into A0. Then, at least in some cases I've looked at, the local cohomology Rtau satifies the equation



Rtau(M)=operatornameRHomA0(operatornameRHomA(M,A),A0)[d](l)



This should be true when the ring A is 'relatively Gorenstein over A0', which means that operatornameExtiA(A0,A) is non-zero for a single i=d, and operatornameExtdA(A0,A)=A(l).



As for translating this to Serre duality, there should be an exact triangle Rtau(M)toMtoRGamma(M)to relating the local cohomology to the derived global sections.

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