Colloquia

Infrared factorization: a practical method for computing two-loop QCD amplitudes

by Prof. Babis Anastasiou (ETH, Zurich)

Europe/Athens
Description

The statistical power of  measurements at the  LHC experiments permits to observe and study are processes. Measurements of  hard scattering hadron collisions with many electroweak bosons, eavy quarks or jets in the final state are important for testing the Standard Model and onstraining its extensions.  Correspondingly, the calculation of perturbative cross-sections for high multiplicity partonic cross-sections is important too. 

In the last five years, groundbreaking results towards next-to-next-to-leading-order (NNLO)  cross-sections for such complicated processes have been derived but there is need for even more powerful methods to combat a  daunting computational cost. 

I will present a novel approach for computing necessary two-loop amplitudes based on QCD factorization, which is a foundanental property of QCD. I will describe the origin of infrared singularities in QCD Feynman diagrams and how they are organised into universal factors in QCD amplitudes. I will then show we can recognise these infrared singular factors in a class of two-loop QCD amplitudes locally and to subtract the singularities away from the integrand. This leads to finite expressions for the physically important and process dependent Factor of the amplitude which describes the hard scattering process.  The latter can be computed with numerical methods, which is an orthogonal approach to traditional  analytic or semianalytic approaches. This work is the first example of a subtraction method for QCD amplitudes beyond the next-to-leading-order and opens the way for building a next generation of computer algorithms for high precision theoretical. Predictions in QCD. 

 

Videoconference via  https://us02web.zoom.us/j/87997630749