Authors:	Baumgart, Stefan
Title:	Effective Field Theories for Physics Beyond the Standard Model
Online publication date:	6-Feb-2020
Language:	english
Abstract:	Under the assumption that the mass scale M of physics beyond the Standard Model (BSM) is far above the electroweak scale v, effective field theories (EFTs) are the suitable method for a consistent separation of the physical processes at these disparate mass scales. We construct EFT frameworks for the generic description of physics BSM - covering the two relevant cases that particles of the BSM sector can or can not be produced on-shell at the Large Hadron Collider (LHC) or a future collider. In the first scenario we focus on the case where a new heavy resonance S with mass MS far above v is discovered at a collider. We assume that the BSM sector contains further yet undiscovered particles with masses of order M ~ MS. We discuss the case where S is a scalar Standard-Model (SM) gauge singlet and formulate an EFT to describe the decays of S into SM particles. We demonstrate that for a consistent separation of the mass scales M and v the appropriate operators in the EFT are non-local Soft-Collinear-Effective- Theory (SCET) operators rather than higher-dimensional local operators. We construct the effective Lagrangian up to the next-to-next-to-leading order in the power-counting parameter v/M and consider the renormalisation-group (RG) equations which allow the resummation of large logarithms of M/v. Our approach provides a template for the construction of analogous EFTs which are suited to describe resonances of different charges and spin. We illustrate our framework in two examples. In the first example we demonstrate that our EFT applies also in the case of the double hierarchy v << MS << M. In the second example we consider a BSM model, where S and heavy, vector-like fermions are added to the SM. We perform the matching of the BSM model to the EFT and show that resummation yields sizeable effects in phenomenologically relevant decay channels. In the second scenario we consider the case where the mass scale M of the BSM model is above the energy reach of the collider. We apply the Standard-Model Effective Theory (SMEFT) in collider studies for the processes dijet- and dilepton production. We derive bounds on the contributing Wilson coefficients and on the mass scale M. For the first time in analyses of this type we employ a consistent expansion in the EFT series in powers of 1/M. We truncate our signal predictions for the cross sections at the next-to-leading order in 1/M and introduce a theory uncertainty to model the terms of higher power. In our analysis we allow for multiple SMEFT operators to contribute at a time. We identify and bound two distinct linear combinations of Wilson coefficients in both studies. The bounds arising in our approach are generically weaker than the overly stringent bounds obtained in previous studies without appropriate theory uncertainties. The method developed in this work can be applied to further processes and the bounds obtained in our approach may serve as an important input for future global fits in the SMEFT framework. The two frameworks developed and applied in this thesis provide a toolbox for the consistent EFT description of BSM physics in the cases described above.
DDC:	530 Physik 530 Physics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 08 Physik, Mathematik u. Informatik
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-2677
URN:	urn:nbn:de:hebis:77-diss-1000033344
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	xiv, 136 Seiten
Appears in collections:	JGU-Publikationen