


(Seminar) The electroweak effective field theory from onshell amplitudes 
CAS Key Laboratory of Theoretical Physics

Institute of Theoretical Physics

Chinese Academy of Sciences

Seminar

Title
题目

The electroweak effective field theory from onshell amplitudes 

Speaker
报告人


Affiliation
所在单位

Technion 
Date
日期

Oct 11th 4:00pm 
Venue
地点

ITP South Building 6520

Abstract
摘要

We apply onshell methods to the bottomup construction of electroweak amplitudes, allowing for both renormalizable and nonrenormalizable interactions. We use the littlegroup covariant massivespinor formalism, and flesh out some of its details along the way. Thanks to the compact form of the resulting amplitudes, many of their properties, and in particular the constraints of perturbative unitarity, are easily seen in this formalism. Our approach is purely bottomup, assuming just the standardmodel electroweak spectrum as well as the conservation of electric charge and fermion number. The most general massive threepoint amplitudes consistent with these symmetries are derived and studied in detail, as the primary building blocks for the construction of scattering amplitudes. We employ a simple argument, based on treelevel unitarity of fourpoint amplitudes, to identify the threepoint amplitudes that are nonrenormalizable at tree level. This bottomup analysis remarkably reproduces many lowenergy relations implied by electroweak symmetry through the standardmodel Higgs mechanism and beyond it. We then discuss fourpoint amplitudes. The gluing of threepoint amplitudes into fourpoint amplitudes in the massive spinor helicity formalism is clarified. As an example, we work out the ycyZh amplitude, including also the nonfactorizable part. The latter is an allorder expression in the effectivefieldtheory expansion. Further constraints on the couplings are obtained by requiring perturbative unitarity. In the ycyZh example, one for instance obtains the renormalizablelevel relations between vector and fermion masses and gauge and Yukawa couplings. We supplement our bottomup derivations with a matching of three and fourpoint amplitude coefficients onto the standardmodel effective field theory (SMEFT) in the broken electroweak phase.

Contact Person
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