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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, 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
URN: urn:nbn:se:kth:diva-154047DOI: 10.1103/PhysRevD.91.075008ISI: 000352786500008OAI: diva2:754862
Swedish Research Council, 621-2011-3985EU, FP7, Seventh Framework Programme, PITN-GA-2011-289442

QC 20141020

Available from: 2014-10-13 Created: 2014-10-13 Last updated: 2015-05-08Bibliographically 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.
TRITA-FYS, ISSN 0280-316X ; 2014:64
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
urn:nbn:se:kth:diva-154048 (URN)978-91-7595-310-6 (ISBN)
2014-10-31, Sal FB42, Roslagstullsbacken 21, Stockholm, 10:00 (English)

QC 20141020

Available from: 2014-10-20 Created: 2014-10-13 Last updated: 2015-03-06Bibliographically approved

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