SciPost Thesis Link
Title:  Higgs Effective Field Theories  Systematics and Applications  
Author:  Claudius Krause  
As Contributor:  Claudius Krause  
Type:  Ph.D.  
Field:  Physics  
Specialties: 


Approaches:  Theoretical, Phenomenological  
URL:  https://doi.org/10.5282/edoc.19873  
Degree granting institution:  LMU Munich  
Supervisor(s):  Gerhard Buchalla  
Defense date:  20160915 
Abstract:
Researchers of the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) announced on July 4th, 2012, the observation of a new particle. The properties of the particle agree, within the relatively large experimental uncertainties, with the properties of the longsought Higgs boson. Particle physicists around the globe are now wondering, "Is it the Standard Model Higgs that we observe; or is it another particle with similar properties?" We employ effective field theories (EFTs) for a general, modelindependent description of the particle. We use a few, minimal assumptions  Standard Model (SM) particle content and a separation of scales to the new physics  which are supported by current experimental results. By construction, effective field theories describe a physical system only at a certain energy scale, in our case at the electroweakscale $v$. Effects of new physics from a higher energyscale, $\Lambda$, are described by modified interactions of the light particles. In this thesis, "Higgs Effective Field Theories  Systematics and Applications", we discuss effective field theories for the Higgs particle, which is not necessarily the Higgs of the Standard Model. In particular, we focus on a systematic and consistent expansion of the EFT. The systematics depends on the dynamics of the new physics. We distinguish two different consistent expansions. EFTs that describe decoupling newphysics effects and EFTs that describe nondecoupling newphysics effects. We briefly discuss the first case, the SMEFT. The focus of this thesis, however, is on the nondecoupling EFTs. We argue that the loop expansion is the consistent expansion in the second case. We introduce the concept of chiral dimensions, equivalent to the loop expansion. Using the chiral dimensions, we expand the electroweak chiral Lagrangian up to nexttoleading order, $\mathcal{O}(f^2/\Lambda^2)=\mathcal{O}(1/16\pi^2)$. Further, we discuss how different assumptions on the custodial symmetry in the Higgs sector influences the list of operators in the basis. Finally, we compare the decoupling and the nondecoupling EFT. We also consider scenarios in which the newphysics sector is nondecoupling at a scale $f$, far above the electroweakscale $v$. We discuss the relevance of the resulting double expansion in $\xi=v^2/f^2$ and$ f^2/\Lambda^2$ for the data analysis at the LHC.In the second part of this thesis, we discuss the applications of the EFTs, especially of the electroweak chiral Lagrangian. First, we connect the EFT with explicit models of new physics. This illustrates how the power counting works in a specific example. We show how different regions of the parameter space of the same model generate a decoupling and a nondecoupling EFT. Second, we use the expansion at leading order to describe the current LHC Higgs data. We show how the current parametrization of the Higgs data, which is used by the experimentalists at CERN (the $\kappa$framework), can be justified quantum field theoretically by the EFT. The result of a fit does therefore not only indicate whether we observe the SMHiggs, but also, in case there are deviations, what kind of new physics is preferred. In this thesis, we fit the data of Run1 (20102013). The effective Lagrangian describing this data can be reduced to six free parameters. The result of this fit is consistent with the SM. It has, however, statistical uncertainties of about ten percent.