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Phenomenology of Neutrino Properties, Unification, and Higgs Couplings

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Doctoral Thesis Phenomenology of neutrino properties, unification, and Higgs couplings beyond the Standard Model Stella Riad Theoretical Particle Physics, Department of Physics, School of Engineering Sciences Royal Institute of Technology, SE-106 91 Stockholm, Sweden Stockholm, Sweden 2017 Typeset in LATEX Akademisk avhandling f¨or avl¨aggande av teknologie doktorsexamen (TeknD) inom ¨amnesomr˚adetfysik. Scientific thesis for the degree of Doctor of Philosophy (PhD) in the subject area of Physics. ISBN 978-91-7729-298-2 TRITA-FYS 2017:10 ISSN 0280-316X ISRN KTH/FYS/{17:10SE c Stella Riad, February 2017 Printed in Sweden by Universitetsservice US AB, Stockholm February 2017 Abstract The vast majority of experiments in particle physics can be described by the Stan- dard 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 of the parameters depends on the model, and thus, it provides a signature of the model. For a model defined at high energies, such as a grand unified theory, it is necessary to run the parameters down to the electroweak scale in order to be able 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, where the extra dimensions are perceived as heavy particles in the four-dimensional theory and we provide an upper limit on the cutoff scale. Furthermore, 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, which was discovered at the Large Hadron Collider (LHC) in 2012, provides new possibilities to study physics beyond the SM. The properties of this boson have to be tested with extremely high precision, at the LHC and possibly in future linear colliders, 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, the Higgs boson may have couplings to new particles, which are not present in the SM. These could, for example, give rise to Higgs lepton flavor violation. We discuss both types of lepton flavor violating processes in the context of the Zee model, a model where neutrino mass is generated at the one-loop level. We find that these can be sizeable and close to the experimental limits. Key words: Effective field theories, neutrino physics, extra dimensions, universal extra dimensions, Higgs physics, renormalization group running, Bayesian statistics, grand unified theories. iii Sammanfattning Standardmodellen f¨or partikelfysik kan beskriva n¨ast intill alla experimentella par- tikelfysikresultat. Men det finns ett antal problem med standardmodellen, som in- neb¨ar att den inte kan vara den slutgiltiga teorin. D¨aremot finns det bara ett k¨ant fel med modellen sj¨alv och det ¨ar att neutriner ¨ar massiva. I standardmodellen ¨ar neutriner n¨amligen massl¨osa. Det finns en m¨angd modeller som beskriver hur ne- utriner kan vara massiva och ge l¨osningar p˚aandra konceptuella problem. I denna avhandling behandlas ett antal s˚adanab˚ade fullst¨andiga och effektiva modeller. V¨ardet p˚astorheter i en modell beror p˚aenerginiv˚an,ett fenomen som kallas renormeringsgruppsl¨opande. Det exakta beroendet varierar och ¨ar p˚as˚as¨att en signatur f¨or den specifika modellen. I modeller som ¨ar definierade vid h¨oga energi- niv˚aer,som exempelvis storf¨orenade teorier, m˚asteparametrarna l¨opa ner till den elektrosvaga energiskalan f¨or att kunna j¨amf¨oras med experimentella resultat. I denna avhandling diskuteras renormeringsgruppsl¨opande i extra dimensioner, d¨ar de extra dimensionerna ist¨allet uppfattas som tunga partiklar i den fyrdimensio- nella v¨arlden och vi kan d¨armed begr¨ansa det omf˚angd¨ar modellen ¨ar giltig. Vi diskuterar ¨aven renormeringsgruppsl¨opandet i tv˚aicke-supersymmetriska SO(10) storf¨orenade teorier samt unders¨oker om, och konstaterar att, de experimentella v¨ardena av massor och blandningsparametrar kan anpassas i modellen. Dessutom diskuteras gaugekopplingarnas l¨opande och m¨ojliga f¨orenande i radiativa neutrino- massmodeller. Vi finner att de kan f¨orenas i ett antal modeller. Det finns andra m¨ojligheter att studera fysik bortom standardmodellen, bland annat genom att studera Higgsbosonen som nyligen uppt¨acktes vid den stora hadron- kollideraren (LHC) i CERN. Innan man med s¨akerhet kan konstatera att denna nya partikel faktiskt ¨ar standardmodellens Higgspartikel m˚astedess egenskaper testas med mycket h¨og precision. Detta kommer att ske i b˚adeLHC och andra framtida experiment. Till exempel m˚asteden nya partikelns kopplingar till de andra par- tiklarna i standardmodellen m¨atas med stor noggrannhet. I denna avhandling g¨or vi bayesisk parameteruppskattning av s˚akallade kopplingsskalfaktorer, som vari- erar storleken p˚aHiggspartikelns kopplingar. Vi j¨amf¨or dessutom modeller, som har ett antal av dessa skalfaktorer som fria parametrar med standardmodellen och finner att resultaten alltid ¨ar till standardmodellens fav¨or. Ut¨over de existerande kopplingarna ¨ar det intressant att unders¨oka om det kan finnas nya kopplingar hos Higgspartikeln. S˚adanakan till exempel ge upphov till smakf¨or¨andrande processer som vi diskuterar i den s˚akallade Zeemodellen d¨ar vi visar att dessa kan vara n¨ara de nuvarande experimentella gr¨anserna. Nyckelord: effektiva f¨altteorier, neutrinofysik, renormeringsgruppsl¨opande, uni- versella extra dimensioner, Higgsfysik, Bayesisk statistik, storf¨orenade teorier. iv Preface This thesis is the result of my research performed at the Department of Theoretical Physics at KTH Royal Institute of Technology from June 2012 to December 2016 and at the Department of Physics at KTH Royal Institute of Technology from January 2017 to February 2017. The thesis is divided into two parts. The first part is an introduction to the subjects relevant for the scientific papers. These subjects include renormalization group running, neutrino physics, extra dimensions, grand unified theories, and Bayesian statistics. The second part consists of the scientific papers that are the result of the research. These are listed below. List of papers included in this thesis [1] T. Ohlsson, and S. Riad Running of Neutrino Parameters and the Higgs Self-Coupling in a Six-Dimensional UED Model Physics Letters B718, 1002-1007 (2012) arXiv:1208.6297 [2] J. Bergstr¨omand S. Riad Bayesian model comparison of Higgs couplings Physical Review D91, 075008 (2015) arXiv:1411.4876 [3] C. Hagedorn, T. Ohlsson, S. Riad, and Michael A. Schmidt Unification of Gauge Couplings in Radiative Neutrino Mass Models Journal of High Energy Physics, 09 (2016) 111 arXiv:1605.03986 [4] D. Meloni, T. Ohlsson, and S. Riad Renormalization Group Running of Fermion Observables in an Extended Non- Supersymmetric SO(10) Model arXiv:1612.07973 [5] J. Herrero-Garcia, T. Ohlsson, S. Riad, and J. Wir´en Full parameter scan of the Zee model: exploring Higgs lepton flavor violation arXiv:1701.05345 v vi Preface List of papers not included in this thesis [6] D. Meloni, T. Ohlsson, and S. Riad Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) model Journal of High Energy Physics, 12 (2014) 052 arXiv:1409.3730 The thesis author's contribution to the papers [1] I performed the analytical and numerical calculations and produced the plots. I wrote the main part of the paper. [2] I implemented the model for use with MultiNest and performed all the numerical fits. I did the model comparison in Sec. 4, produced some of the figures, and wrote parts of the paper. [3] I performed all of the numerical computations for the RG running of the gauge couplings and checked parts of the analytical computations. I wrote parts of the paper. [4] The RGEs were partially computed analytically by me and derived partially by me using the software SARAH. I implemented the model for use with MultiNest and performed the numerical fits in both the minimal and the extended model. I wrote parts of the paper and produced all figures. [5] The model was partially implemented by me for use with MultiNest.I performed all of the numerical fits and produced the figures. I checked some of the analytical calculations and wrote parts of the paper. Acknowledgements First, I would like to thank my supervisor Tommy Ohlsson, who has given me the opportunity to carry out research in the incredibly interesting field of theoretical elementary particle physics. Thanks for the scientific collaboration that lead to four of the papers included in this thesis, for all of the advice given through the years, and for the careful proofreading of this thesis. My warmest thanks to Davide Meloni for the collaboration that lead to one paper included in this thesis and for the many discussions we've had over the years. Special thanks to Johannes Bergstr¨om,Claudia Hagedorn, Michael A. Schmidt, Juan Herrero-Garc´ıa,and Jens Wir´enfor fruitful discussions and collaborations that resulted in papers included in this thesis. I would also like to thank Johannes, Juan, and Jens for being such great office mates.
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