Speaker: Camila Machado, IFT-UNESP

When/Where: 4:30 PM, October 26, 2016 (Sala 210)

Abstract: The Feynman rules appear as a simple way to calculate scattering
amplitudes, however some complications appear if the multiplicity of
particles is large. For example, in the 2 to 2 scattering of gluons
there are only 4 Feynman diagrams but if we add two extra gluons it
grows to 220 diagrams. In the 80’s Stephen Parke and Tomasz Taylor
found an incredible way to simplify the calculation of some classes of
n-gluons scattering amplitudes based on helicity arguments. Since
then, a lot of progress has been made on improving the amplitude
techniques and on the understanding of the S-matrix physics.
After a review of the spinor helicity formalism and some well known
results based on it, I will discuss how we can use the helicity
structure of scattering amplitudes in the SM and in the context of an
effective Lagrangian description of BSM dynamics. The analysis reveals
a novel set of helicity selection rules according to which, in the
majority of 2 to 2 scattering processes at high energy, the SM and the
leading BSM effects do not interfere. This have a big impact on how we
should perform the EFT analysis and where we should search for new
physics.