Non-crossing chord diagram characterization of phi^4 regions

Let nn be even. Place n2n-2 ordered points labeled 3,4,cldots,n3,4,cldots,n on a line, and let cthetaabctheta_{ab} denote a chord in a non-crossing perfect matching. For x=(x0,cldots,xn3)cincmathbbRn2x=(x_0,cldots,x_{n-3})cincmathbb{R}^{n-2}, define

H(x)=csuma=0n3xa+2csuma=0n4csumb=a+1n3(1)bacmin(xa,xa+1,cldots,xb).H(x)=csum_{a=0}^{n-3}x_a+2csum_{a=0}^{n-4}csum_{b=a+1}^{n-3}(-1)^{b-a}cmin(x_a,x_{a+1},cldots,x_b).

Non-crossing chord diagram conjecture. The regions contributing to Anϕ4A_n^{\phi^4} are in bijection with the Cn/21C_{n/2-1} possible non-crossing chord diagrams. The region associated with a diagram satisfies xa3=xb3x_{a-3}=x_{b-3} for each chord cthetaabctheta_{ab}, and xa3=xb3<xc3=xd3x_{a-3}=x_{b-3}<x_{c-3}=x_{d-3} whenever cthetaabctheta_{ab} surrounds cthetacdctheta_{cd}; equivalently, these regions are all solutions to H(x)=0H(x)=0.

The paper explicitly states that this conjecture is proved later in the paper, so its database status is solved.

Sources & referencesView supporting material

Primary source

Bruno Giménez Umbert and Karen Yeats, “Φ^p Amplitudes from the Positive Tropical Grassmannian: Triangulations of Extended Diagrams”, arXiv:2403.17051 (2024).

Additional references

2 papers in this index state this conjecture (2022–2024). The statement above is taken from the most recent of them; the others are arXiv:2205.02722.

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