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Non-unitary neutrino mixing from an extra-dimensional seesaw model
Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), München, Germany.ORCID iD: 0000-0001-5948-9152
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics. (Theoretical Particle Physics)
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.ORCID iD: 0000-0002-3525-8349
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

We study the generation of light neutrino masses in an extra-dimensional model, where right-handed neutrinos are allowed to propagate in the extra dimension, while the Standard model (SM) particles are confined to a brane. Motivated by the fact that extra-dimensional models are non-renormalizable, we truncate the Kaluza–Klein (KK) towers at a maximal KK index. The structure of the bulk Majorana mass term, motivated by the Sherk–Schwarz mechanism, implies that the right-handed KK neutrinos pair to form Dirac neutrinos, except for a number of unpaired Majorana neutrinos at the top of each tower. These heavy Majorana neutrinos are the only sources of lepton number breaking in the model, and similarly to the type-I seesaw mechanism, they naturally generate small masses for the left-handed neutrinos. The lower KK modes mix with the light neutrinos, and the mixing effects are not suppressed with respect to the light neutrino masses. Compared to conventional fermionic seesaw models, the non-unitary effects induced by such mixing are quite significant. We study the signals of this model at the Large Hadron Collider (LHC), and find that the current bounds on the non-unitarity parameters are strong enough to exclude an observation.

Place, publisher, year, edition, pages
National Category
Subatomic Physics
URN: urn:nbn:se:kth:diva-31716OAI: diva2:406049
Swedish Research Council, 621-2008-4210EU, FP7, Seventh Framework Programme
QC 20110324. Manuskriptet har uppdaterats och publicerats som "Signatures from an extra-dimensional seesaw model" i PHYSICAL REVIEW D, 2010, Vol 82,Issue 4. The submitted manuscript has been peer-reviewed and published under the title "Signatures from an extra-dimensional seesaw model" in PHYSICAL REVIEW D, 2010, Vol 82,Issue 4.Available from: 2011-06-21 Created: 2011-03-24 Last updated: 2012-03-15Bibliographically approved
In thesis
1. Astrophysical and Collider Signatures of Extra Dimensions
Open this publication in new window or tab >>Astrophysical and Collider Signatures of Extra Dimensions
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In recent years, there has been a large interest in the subject of extra dimensions in particle physics. In particular, a number of models have been suggested which provide solutions to some of the problems with the current Standard Model of particle physics, and which could be tested in the next generation of high-energy experiments. Among the most important of these models are the large extra dimensions model by Arkani-Hamed, Dimopoulos, and Dvali, the universal extra dimensions model, and models allowing right-handed neutrinos to propagate in the extra dimensions. In this thesis, we study phenomenological aspects of these three models, or simple modifications of them.


The Arkani-Hamed-Dimopoulos-Dvali model attempts to solve the gauge hierarchy problem through a volume suppression of Newton's gravitational constant, lowering the fundamental Planck scale down to the electroweak scale. However, this solution is unsatisfactory in the sense that it introduces a new scale through the radius of the extra dimensions, which is unnaturally large compared to the electroweak scale. It has been suggested that a similar model, with a hyperbolic internal space, could provide a more satisfactory solution to the problem, and we consider the hadron collider phenomenology of such a model.


One of the main features of the universal extra dimensions model is the existence of a potential dark matter candidate, the lightest Kaluza-Klein particle. In the so-called minimal universal extra dimensions model, the identity of this particle is well defined, but in more general models, it could change. We consider the indirect neutrino detection signals for a number of different such dark matter candidates, in a five- as well as a six-dimensional model.


Finally, right-handed neutrinos propagating in extra dimensions could provide an alternative scenario to the seesaw mechanism for generating small masses for the left-handed neutrinos. Since extra-dimensional models are non-renormalizable, the Kaluza-Klein tower is expected to be cut off at some high-energy scale. We study a model where a Majorana neutrino at this cutoff scale is responsible for the generation of the light neutrino masses, while the lower modes of the tower could possibly be observed in the Large Hadron Collider. We investigate the bounds on the model from non-unitarity effects, as well as collider signatures of the model.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2010. 68 p.
Trita-FYS, ISSN 0280-316X ; 2010:05
Extra-dimensional quantum field theories, universal extra dimensions, Kaluza-Klein dark matter, Arkani-Hamed-Dimopoulos-Dvali model, hierarchy problem, neutrino mass, seesaw mechanism, Large Hadron Collider phenomenology
National Category
Subatomic Physics
urn:nbn:se:kth:diva-11968 (URN)978-91-7415-556-3 (ISBN)
2010-02-19, FB53, Albanova, Roslagstullsbacken 21, 106 91 Stockholm, 10:00 (English)
QC 20110324Available from: 2010-02-05 Created: 2010-02-02 Last updated: 2011-03-24Bibliographically approved

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