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Astrophysical and Collider Signatures of Extra Dimensions
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics. (Theoretical Particle Physics)
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.
Series
Trita-FYS, ISSN 0280-316X ; 2010:05
Keyword [en]
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
Identifiers
URN: urn:nbn:se:kth:diva-11968ISBN: 978-91-7415-556-3 (print)OAI: oai:DiVA.org:kth-11968DiVA: diva2:291575
Presentation
2010-02-19, FB53, Albanova, Roslagstullsbacken 21, 106 91 Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110324Available from: 2010-02-05 Created: 2010-02-02 Last updated: 2011-03-24Bibliographically approved
List of papers
1. Searches for hyperbolic extra dimensions at the LHC
Open this publication in new window or tab >>Searches for hyperbolic extra dimensions at the LHC
2008 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2008, no 08, 077- p.Article in journal (Refereed) Published
Abstract [en]

We investigate a model of large extra dimensions where the internal space has the geometry of a hyperbolic disc. Compared with the ADD model, this model provides a more satisfactory solution to the hierarchy problem between the electroweak scale and the Planck scale, and it also avoids constraints from astrophysics. In general, a novel feature of this model is that the physical results depend on the position of the brane in the internal space, and in particular, the signal almost disappears completely if the brane is positioned at the center of the disc. Since there is no known analytic form of the Kaluza-Klein spectrum for our choice of geometry, we obtain a spectrum based on a combination of approximations and numerical computations. We study the possible signatures of our model for hadron colliders, especially the LHC, where the most important processes are the production of a graviton together with a hadronic jet or a photon. We find that the signals are similar to those of the ADD model, regarding both qualitative behavior and strength. For the case of hadronic jet production, it is possible to obtain relatively strong signals, while for the case of photon production, this is much more difficult.

Place, publisher, year, edition, pages
IOP Publishing, 2008
Keyword
large extra dimensions, hadronic colliders, space dimensions, millimeter, hierarchy, gravity, signals
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-17796 (URN)10.1088/1126-6708/2008/08/077 (DOI)000258917400032 ()2-s2.0-54749115150 (Scopus ID)
Funder
Swedish Research Council, 621-2005-3588
Note
QC 20100525Available from: 2011-06-21 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Neutrinos from Kaluza-Klein dark matter in the Sun
Open this publication in new window or tab >>Neutrinos from Kaluza-Klein dark matter in the Sun
2010 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, Vol. 2010, no 01, 018- p.Article in journal (Refereed) Published
Abstract [en]

We investigate indirect neutrino signals from annihilations of Kaluza-Klein dark matter in the Sun. Especially, we examine a five- as well as a six-dimensional model, and allow for the possibility that boundary localized terms could affect the spectrum to give different lightest Kaluza-Klein particles, which could constitute the dark matter. The dark matter candidates that are interesting for the purpose of indirect detection of neutrinos are the first Kaluza-Klein mode of the U(1) gauge boson and the neutral component of the SU(2) gauge bosons. Using the DarkSUSY and WimpSim packages, we calculate muon fluxes at an Earth-based neutrino telescope, such as IceCube. For the five-dimensional model, the results hat we obtained agree reasonably well with the results that have previously been presented in the literature, whereas for the six-dimensional model, we find that, at tree-level, the results are the same as for the five-dimensional model. Finally, if the first Kaluza-Klein mode of the U(1) gauge boson constitutes the dark matter, IceCube can constrain the parameter space. However, in the case that the neutral component of the SU(2) gauge bosons is the LKP, the signal is too weak to be observed.

Place, publisher, year, edition, pages
IOP Publishing / SISSA, 2010
Keyword
dark matter theory, extra dimensions, neutrino astronomy
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-31713 (URN)10.1088/1475-7516/2010/01/018 (DOI)000289245200008 ()
Funder
Swedish Research Council, 623-2007-8066Swedish Research Council, 621-2005-3588Swedish Research Council, 621-2008-4210
Note
QC 20110324Available from: 2011-06-21 Created: 2011-03-24 Last updated: 2012-04-27Bibliographically approved
3. Non-unitary neutrino mixing from an extra-dimensional seesaw model
Open this publication in new window or tab >>Non-unitary neutrino mixing from an extra-dimensional seesaw model
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.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-31716 (URN)
Funder
Swedish Research Council, 621-2008-4210EU, FP7, Seventh Framework Programme
Note
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

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