Speaker
Description
Evanescent integrals are those whose integrands vanish when considered on loop momentum configurations that are strictly four-dimensional. They naturally span the space of dimensionally-regulated integrals that are missed when performing four-dimensional unitarity cuts. Such integrals are well understood at one loop, where they give rise to the so-called "rational part" of the amplitude. In this talk, we discuss a new approach to computing evanescent integrals that generalizes to the two-loop level. Our method makes use of the local counterterm formalism of Anastasiou and Sterman, which we use to show that these integrals can be broken down into contributions from soft, collinear and ultra-violet regions. These contributions are much simpler than the original two-loop integral: they take the form of products of one-loop integrals, or one-fold integrals over one-loop integrals. To demonstrate the power of our approach, we apply it to the two-loop five-point all-plus amplitude and find that at both one and two loops the finite remainder is given by only ultra-violet contributions.
