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Bayesian Model comparison of Higgs couplings
Universitat de Barcelona.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
2015 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 7, 075008Article in journal (Refereed) Published
Abstract [en]

We investigate the possibility of contributions from physics beyond the Standard Model (SM) to the Higgs couplings, in the light of the LHC data. The work is performed within an interim framework where the magnitude of the Higgs production and decay rates are rescaled through Higgs coupling scale factors. We perform Bayesian parameter inference on these scale factors, concluding that there is good compatibility with the SM. Furthermore, we carry out a Bayesian model comparison on all models where any combination of scale factors can differ from their SM values and find that typically models with fewer free couplings are strongly favored. We consider the evidence that each coupling individually equals the SM value, making the minimal assumptions on the other couplings. Finally, we make a comparison of the SM against a single "not-SM" model and find that there is moderate to strong evidence for the SM.

Place, publisher, year, edition, pages
2015. Vol. 91, no 7, 075008
Keyword [en]
Massless Particles, Broken Symmetries, Atlas Detector, Lhc, Boson, Curvature, Cosmology, Inference, Efficient, Tevatron
National Category
Subatomic Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-154047DOI: 10.1103/PhysRevD.91.075008ISI: 000352786500008OAI: oai:DiVA.org:kth-154047DiVA: diva2:754862
Funder
Swedish Research Council, 621-2011-3985EU, FP7, Seventh Framework Programme, PITN-GA-2011-289442
Note

QC 20141020

Available from: 2014-10-13 Created: 2014-10-13 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Studies of effective theories beyond the Standard Model
Open this publication in new window or tab >>Studies of effective theories beyond the Standard Model
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The vast majority of all experimental results in particle physics can be described by the Standard Model (SM) of particle physics. However, neither the existence of neutrino masses nor the mixing in the leptonic sector, which have been observed, can be described within this model. In fact, the model only describes a fraction of the known energy in the Universe. Thus, we know there must exist a theory beyond the SM. There is a plethora of possible candidates for such a model, such as supersymmetry, extra dimensional theories, and string theory. So far, there are no evidence in favor of these models.

These theories often reside at high energies, and will therefore be manifest as effective theories at the low energies experienced here on Earth. A first example in extra-dimensional theories. From our four-dimensional point of view, particles which propagate through the extra dimensions will effectivel be perceived as towers of heavy particles. In this thesis we consider an extra-dimensional model with universal extra dimensions, where all SM particles are allowed to propagate through the extra dimensions. Especially, we place a bound on the range of validity for this model. We study the renormalization group running of the leptonic parameters as well as the Higgs self-coupling in this model with the neutrino masses generated by a Weinberg operator.

Grand unified theories, where the gauge couplings of the SM are unified into a single oe at some high energy scale, are motivated by the electroweak unification. The unification must necessarily take place at energies many orders of magnitude greater than those that ever can be achieved on Earth. In order to make sense of the theoru, ehich is given at the grand unified scale, at the electroweak scale, the symmetry at the grand unified scale is broken down to the SM symmetry. Within these models the SM is considered as an effective field theory. We study renormalization group running of the leptonic parameters in a non-supersymmetric SO(10) model which is broken in two steps via the Pati-Salam group.

Finally, the discovery of the new boson at the LHC provides a new opportunity to search for physics beyond the SM. We consider an effective model where the magnitudes of the couplings in the Higgs sector are scaled by so-called coupling scale factors. We perform Bayesian parameter inference based on the LHC data. Furthermore, we perform Bayesian model comparison, comparing models where one or several of the Higgs couplings are allowed, to the SM, where the couplings are fixed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. x, 64 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2014:64
Keyword
Effective field theories, neutrino physics, extra dimensions, universal extra dimensions, Higgs physics, renormalization group running, Bayesian statistics, coupling scale factor, grand unified theories
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-154048 (URN)978-91-7595-310-6 (ISBN)
Presentation
2014-10-31, Sal FB42, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20141020

Available from: 2014-10-20 Created: 2014-10-13 Last updated: 2015-03-06Bibliographically approved
2. Phenomenology of neutrino properties, unification, and Higgs couplings beyond the Standard Model
Open this publication in new window or tab >>Phenomenology of neutrino properties, unification, and Higgs couplings beyond the Standard Model
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The vast majority of experiments in particle physics can be described by the Standard Model of particle physics (SM). However, there are indications for physics beyond it. The only experimentally demonstrated problem of the model is the difficulty to describe neutrino masses and leptonic mixing. There is a plethora of models that try to describe these phenomena and this thesis investigates several possibilities for new models, both full theories and effective frameworks.

 

The values of the parameters in a model are dependent on the energy scale and we say that the parameters run. The exact behavior of the running depends on the model and it provides a signature of the model. For a model defined at high energies it is necessary to run the parameters down to the electroweak scale in order to perform a comparison to the known values of observed quantities. In this thesis, we discuss renormalization group running in the context of extra dimensions and we provide an upper limit on the cutoff scale. We perform renormalization group running in two versions of a non-supersymmetric SO(10) model and we show that the SM parameters can be accommodated in both versions. In addition, we perform the running for the gauge couplings in a large set of radiative neutrino mass models and conclude that unification is possible in some of them.

 

The Higgs boson provides new possibilities to study physics beyond the SM. Its properties have to be tested with extremely high precision before it could be established whether the particle is truly the SM Higgs boson or not. In this thesis, we perform Bayesian parameter inference and model comparison. For models where the magnitude of the Higgs couplings is varied, we show that the SM is favored in comparison to all other models. Furthermore, we discuss lepton flavor violating processes in the context of the Zee model. We find that these can be sizeable and close to the experimental limits.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 98 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2017:10
Keyword
Effective field theories, neutrino physics, extra dimensions, universal extra dimensions, Higgs physics, renormalization group running, Bayesian statistics, grand unified theories
National Category
Subatomic Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-202311 (URN)978-91-7729-298-2 (ISBN)
Public defence
2017-03-24, FB53, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170221

Available from: 2017-02-21 Created: 2017-02-20 Last updated: 2017-02-23Bibliographically approved

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