Cluster Algebras in Kinematic Space of Scattering Amplitudes

Abstract: We clarify the natural cluster algebra of type A that exists in a residual and tropical form in the kinematical space as suggested in 1711.09102 by the use of triangulations, mutations and associahedron on the definition of scattering forms. We also show that this residual cluster algebra is preserved in a hypercube (diamond) necklace inside the associahedron where cluster sub-algebras $(A_1)^n$ exist. This result goes in line with results with cluster poligarithms in 1401.6446 written in terms of $A_2$ and $A_3$ functions only and other works showing the primacy of $A$ cluster sub-algebras as data input for scattering amplitudes.