Compatible Cycles and CHY Integrals

Abstract

The CHY construction naturally associates a vector in ${\mathbb{R}}^{(n-3)!}$ to every 2-regular graph with $n$ vertices. Partial amplitudes in the biadjoint scalar theory are given by the inner product of vectors associated with a pair of cycles. In this work we study the problem of extending the computation to pairs of arbitrary 2-regular graphs. This requires the construction of compatible cycles, i.e. cycles such that their union with a 2-regular graph admits a Hamiltonian decomposition. We prove that there are at least $(n-2)!/4$ such cycles for any 2-regular graph. We also find a connection to breakpoint graphs when the graph only has double edges. We end with a comparison of the lower bound on the number of randomly selected cycles needed to generate a basis of ${\mathbb{R}}^{(n-3)!}$, using the super Catalan numbers, and our lower bound for compatible cycles.

20 pages, added some graph theory background definitions

References in corpus (2)

• Two-Loop Scattering Amplitudes from the Riemann Sphere
• Manifesting Color-Kinematics Duality in the Scattering Equation Formalism

Cited by in corpus (2)

• One-loop diagrams with quadratic propagators from the worldsheet
• One-loop CHY-Integrand of Bi-adjoint Scalar Theory