Séminaire Lotharingien de Combinatoire, 89B.71 (2023), 12 pp.
Maria Gillespie and Andrew Reimer-Berg
A Generalized RSK for Enumerating Linear Series on n-pointed Curves
Abstract.
We give a combinatorial proof of a recent geometric result of Farkas and Lian on linear series on curves with prescribed incidence conditions. The result states that the expected number of degree-d morphisms from a general genus-g, n-marked curve C to Pr, sending the marked points on C to specified general points in Pr, is equal to
(r+1)g for sufficiently large d. This computation may be rephrased as an intersection problem on Grassmannians, which has a combinatorial interpretation in terms of Young tableaux by the Littlewood-Richardson rule. We give a bijection, generalizing the RSK correspondence, between the tableaux in question and the (r+1)-ary sequences of length g, and we explore our bijection's combinatorial properties.
We also apply similar methods to give a combinatorial interpretation and proof of the fact that, in the modified setting in which r=1 and several marked points map to the same point in P1, the number of morphisms is still
2g for sufficiently large d.
Received: November 15, 2022.
Accepted: February 20, 2023.
Final version: April 1, 2023.
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