Fuss–Catalan enumeration and construction of regions for AnϕpA^{\phi^p}_n

Place n2n-2 points labeled 0,1,,n30,1,\ldots,n-3 in increasing order on the real line, and let H(x)H(x) be the function in the global Schwinger formula for AnϕpA^{\phi^p}_n. For a non-crossing (p2)(p-2)-chord θa1,a2,,ap2\theta_{a_1,a_2,\ldots,a_{p-2}}, associate the equalities xa1=xa2==xap2x_{a_1}=x_{a_2}=\cdots=x_{a_{p-2}}; if it surrounds θb1,b2,,bp2\theta_{b_1,b_2,\ldots,b_{p-2}}, impose the corresponding strict inequality between the two common values. Fuss–Catalan region conjecture. The regions contributing to AnϕpA^{\phi^p}_n are in bijection with the FC(n2)/(p2)(p2,1)\textrm{FC}_{(n-2)/(p-2)}(p-2,1) possible non-crossing (p2)(p-2)-chord diagrams, and the region associated with each diagram is obtained by these equalities and nesting inequalities. These regions are all the solutions to H(x)=0H(x)=0, and their contributions produce all the FC(n2)/(p2)(p1,1)\textrm{FC}_{(n-2)/(p-2)}(p-1,1) trees of ϕp\phi^p. The supplied text gives no evidence that this conjectural classification and enumeration has been resolved.

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Primary source

Freddy Cachazo and Bruno Giménez Umbert, “Connecting Scalar Amplitudes using The Positive Tropical Grassmannian”, arXiv:2205.02722 (2022).

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