Building locally finite two-loop QCD amplitudes

by Babis Anastasiou (ETH Zürich)

Main auditorium hall (MPP)

Main auditorium hall


The Large Hadron Collider (LHC) experiments have remarkable
statistical power that enables the observation and study of rare
processes. Measurements of hard scattering in hadron collisions with
multiple electroweak bosons, heavy quarks, or jets in the final state
play a critical role in testing the Standard Model and constraining
its extensions. In the last five years, significant progress has been made in deriving
next-to-next-to-leading-order (NNLO) cross-sections for these complex
processes, but the computational cost remains a challenge.
In this presentation, we introduce a novel approach for computing necessary two-loop amplitudes based on QCD factorization. We discuss the origin of infrared singularities in QCD Feynman diagrams and how they can be organized into universal factors in QCD amplitudes. We demonstrate that we can identify these infrared singular factors in a class of two-loop QCD amplitudes, subtracting them from the integrand and leading to finite expressions for the physically significant and process-dependent factor of the amplitude that describes the hard scattering process. The latter can be computed with numerical methods, which is a complementary approach to traditional analytic or semi-analytic methods. This work represents the first example of a subtraction method for QCD amplitudes beyond the next-to-leading-order and paves the way for building the next generation of computer algorithms for high-precision theoretical predictions in QCD.