#### Comparing high-energy with infrared factorisations in four-parton scattering amplitudes in QCD

- Event time: 2:00pm
- Event date: 15th October 2014
- Speaker: Leonardo Vernazza (Formerly School of Physics & Astronomy, University of Edinburgh)
- Location: Higgs Centre Seminar Room, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB

### Event details

I will discuss our recent study of the high-energy limit of four-parton scattering amplitudes in QCD, giving explicit results at two loops and higher orders, and going beyond next-to-leading logarithmic (NLL) accuracy. I will show how techniques of infrared factorisation can be used to investigate the failure of the simplest form of Regge factorization, starting at next-to-next-to-leading logarithmic accuracy (NNLL) in ln(s/|t|). I will provide detailed accounts and explicit expressions for the terms responsible for this breaking in the case of two-loop and three-loop quark and gluon amplitudes in QCD; in particular, I will discuss how a known non-logarithmic double-pole contribution at two-loops can be recovered and explained. I will show results for all non-factorizing single-logarithmic singular contributions at three loops. Conversely, I will explain how high-energy factorisation can be used to show that the hard functions of infrared factorization vanish in d = 4 to all orders in the coupling, up to NLL accuracy in ln(s/|t|). This provides clear evidence for the infrared origin of high-energy logarithms. Finally, I discuss the extension of earlier studies to t-channel exchanges of color representations beyond the octet, which enables me to give predictions based on the dipole formula for single-pole NLL contributions at three and four loops.

The Particle Physics Theory seminar is a weekly series of talks reflecting the diverse interests of the group. Topics include analytic and numerical calculations based on the Standard Model of elementary particle physics, theories exploring new physics, as well as more formal developments in gauge theories and gravity..