New quantum field theory methods for collider physics and strongly coupled systems

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Searching for new physics requires ever more accurate understanding and modeling of the already known Standard Model of particles. It is also important to know where to look for new physics. In this thesis we will discuss investigations that address each of the aforementioned challenges. To model the dominant QCD backgrounds of the Standard Model more accurately it is important to use exact QCD matrix elements in the parton shower modeling. We will show that a helicity dependent unitary parton shower can achieve efficient matching with exact tree-level QCD matrix elements. The second challenge of knowing where to look for new physics is a daunting task. The Standard Model is a consistent theory all the way up to the GUT scale and using naturalness (absence of fine tuning) as a guideline for where to find new physics is proving increasingly nebulous. To locate physics beyond the Standard Model, we need something that takes us out of the standard model, and this is provided by dark matter. Perturbative unitarity can place interesting bounds on the scale of new physics for any Beyond the Standard Model theory that incorporates dark matter. Using the example of the Next to Minimally Supersymmetric Standard Model (NMSSM), we will show that perturbative unitarity combined with some basic hypothesis about dark matter can tell us where the next scale of new physics could be in a reliable way. In the last part of the thesis, we will discuss how the principle of perturbative unitarity can be applied to strongly coupled systems. A strongly coupled system with conformal symmetry admits an effective description if there is a large dimension gap in the spectrum of the dilatation operator and a parameter such as 1/N that suppresses higher point connected functions. In this case, the three-point current correlation function of a strongly coupled system with conformal symmetry can be calculated from the dual weakly coupled AdS effective theory. The three-point function admits perturbative expansion in the inverse dimension gap. The contribution from the first non-renormalizable bulk operator is computed and shown to lead to a different polarization structure compared to the leading renormalizable operator. This result is used to suggest an experimental probe of the effective description of strongly coupled systems at second order phase transition through an indirect measurement of the the dimension gap.


Type of resource text
Form electronic; electronic resource; remote
Extent 1 online resource.
Publication date 2014
Issuance monographic
Language English


Associated with Betre, Kassahun
Associated with Stanford University, Department of Physics.
Primary advisor Peskin, Michael Edward, 1951-
Thesis advisor Peskin, Michael Edward, 1951-
Thesis advisor Hewett, JoAnne L
Thesis advisor Senatore, Leonardo
Advisor Hewett, JoAnne L
Advisor Senatore, Leonardo


Genre Theses

Bibliographic information

Statement of responsibility Kassahun Betre.
Note Submitted to the Department of Physics.
Thesis Thesis (Ph.D.)--Stanford University, 2014.
Location electronic resource

Access conditions

© 2014 by Kassahun Haileyesus Betre
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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