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Authors: Aoude, Rafael
Title: Effective Field Theory Phenomenology and Scattering Amplitudes
Online publication date: 11-Nov-2020
Language: english
Abstract: The Standard Model (SM) is an effective description of Nature and experimental evidences indicates that beyond SM physics ought to exist. The series of the LHC null results for many searches for specific models have shifted the interest towards a model-independent effective description. Effective Field Theories (EFTs) provide a framework not only to parametrize the unknown but also to make efficient calculations with the right degrees of freedom. The most simple candidate for an effective extension of the SM is called Standard Model Effective Field Theory (SMEFT), which assumes that the scalar boson discovered by the LHC belongs to a doublet under the SM Electroweak symmetry. This thesis focuses on the study of the SMEFT via phenomenological imprints at the LHC and using new modern methods for scattering amplitudes. In the first part, we study the diboson production at the LHC and the impact of flavour data in SMEFT global fits. The former probes the nature of the electroweak symmetry breaking mechanism via anomalous triple-gauge-couplings and can be studied with an observable sensitive to only one higher-dimensional operator, which is rare in LHC SMEFT signals. Using jet substructure techniques, we analyse the azimuthal angles of the hadronic and semileptonic diboson production final states. In the latter, we study how flavour data can constrain the unknown parameters of SMEFT, the Wilson coefficients. Flavour low-energy measurements are known to put strong bounds on deviations of the SM flavour structure. Usually, these bounds are avoided in model building by assuming some kind of flavour symmetry in the ultraviolet. We study two flavour assumptions: leading-order Minimal Flavour Violation and U(3)$^5$. We show that the flavour data still put strong constraints on models of new physics, even in the most flavourless scenario. Global fits are of extreme importance for model building since a lot of new physics models can be matched to SMEFT. The bounds on the Wilson Coefficients set the allowed space of the EFT and, consequently, on the allowed parameter space of the respective model. In the second part, we use modern methods for scattering amplitudes to study the SMEFT. These new methods rely on spinor-helicity variables, recursion relations and generalized unitarity. They provide efficient tools to calculate higher-multiplicity and multi-loops amplitudes. We study the three-point SMEFT amplitudes in a new covariant massive spinor-helicity formalism and discuss the construction of higher point amplitudes via recursion relations and consistent factorization. The results on massive on-shell SMEFT amplitudes will allow precise computations in this EFT for the LHC.
DDC: 530 Physik
530 Physics
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 08 Physik, Mathematik u. Informatik
Place: Mainz
Version: Original work
Publication type: Dissertation
License: in Copyright
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Extent: 153 Seiten
Appears in collections:JGU-Publikationen

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