Traintracks All the Way Down

Abstract

We study the class of planar Feynman integrals that can be constructed by sequentially intersecting traintrack diagrams without forming a closed traintrack loop. After describing how to derive a $2L$-fold integral representation of any $L$-loop diagram in this class, we provide evidence that their leading singularities always give rise to integrals over $(L{-}1)$-dimensional varieties for generic external momenta, which for certain graphs we can identify as Calabi-Yau $(L{-}1)$-folds. We then show that these diagrams possess an interesting nested structure, due to the large number of second-order differential operators that map them to (products of) lower-loop integrals of the same type.