Multiplicity inequality for simple transversal modules on a non-commutative smooth surface

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Let AA be the graded algebra defining the non-commutative smooth surface X=Proj⁡AX=\operatorname{Proj} A, let Y=Proj⁡A/gAY=\operatorname{Proj} A/gA be the divisor defined by the central degree-three element gg, and let trans⁡Y(X)\operatorname{trans}_Y(X) denote the class of objects transverse to YY. For M∈trans⁡Y(X)\mathcal M\in\operatorname{trans}_Y(X), write rp,n=rp,n(M)r_{p,n}=r_{p,n}(\mathcal M) for the multiplicities of the points infinitely near to p∈Yp\in Y, and write e=e(M)e=e(\mathcal M) for its multiplicity. Assume that the image of M\mathcal M in mod⁡(X)/Cf\operatorname{mod}(X)/\mathcal C_f is simple.

Multiplicity inequality. The following inequality holds:

∑p,nrp,n(rp,n−1)2≤(e−1)(e−2)2.\sum_{p,n} \frac{r_{p,n}(r_{p,n}-1)}{2}\leq \frac{(e-1)(e-2)}{2}.

This is presented as a conjectural analogue of the corresponding multiplicity bound for objects on commutative smooth surfaces. The supplied source does not state whether the inequality has been proved or disproved, so its status remains open.

References

Primary source

Michel Van den Bergh, “Blowing up non-commutative smooth surfaces”, arXiv:math/9809116 (1998).

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