Loops without loops and the Feynman tree

Tuesday, 20 November 2018 at 11:15, in Y16 G05 - Campus Irchel

Quantum field theory is poorly defined in four space-time dimensions  due to unphysical configurations introduced by quantum corrections.  These unphysical configurations lead to the proliferation of  infinities that are usually regulated by modifying the dimensions of  the space-time. In this talk we introduce the loop-tree duality (LTD)  and the four-dimensional unsubtraction (FDU) formalisms.The LTD allows to rewrite loop scattering amplitudes in terms of  connected tree-level dual amplitudes, and provides a very intuitive  view over the origin of the IR and UV singularities and their  interpretation in terms of causality.  We also comment on its relation  to the Feynman’s Tree Theorem. The FDU allows to perform the summation  over soft and collinear degenerate states from virtual and real  configurations by introducing a suitable mapping of momenta, then  avoiding subtractions in the infrared in such a way that higher order  perturbative calculations can directly be performed in four space-time  dimensions. We illustrate the power of the formalism with benchmark  physical examples.