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.