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Predictions of Effective Models in Neutrino Physics
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Experiments on neutrino oscillations have confirmed that neutrinos have small, but non-zero masses, and that the interacting neutrino states do not have definite masses, but are mixtures of such states.The seesaw models make up a group of popular models describing the small neutrino masses and the corresponding mixing.In these models, new, heavy fields are introduced and the neutrino masses are suppressed by the ratio between the electroweak scale and the large masses of the new fields. Usually, the new fields introduced have masses far above the electroweak scale, outside the reach of any foreseeable experiments, making these versions of seesaw models essentially untestable. However, there are also so-called low-scale seesaw models, where the new particles have masses above the electroweak scale, but within the reach of future experiments, such as the LHC.In quantum field theories, quantum corrections generally introduce an energy-scale dependence on all their parameters, described by the renormalization group equations. In this thesis, the energy-scale dependence of the neutrino parameters in two low-scale seesaw models, the low-scale type I and inverse seesaw models, are considered. Also, the question of whether the neutrinos are Majorana particles, \ie , their own antiparticles, has not been decided experimentally. Future experiments on neutrinoless double beta decay could confirm the Majorana nature of neutrinos. However, there could also be additional contributions to the decay, which are not directly related to neutrino masses. We have investigated the possible future bounds on the strength of such additional contributions to neutrinoless double beta decay, depending on the outcome of ongoing and planned experiments related to neutrino masses.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology , 2011. , xii, 64 p.
Series
Trita-FYS, ISSN 0280-316X ; 2011:31
Keyword [en]
Neutrino mass, lepton mixing, Majorana neutrinos, effective field theory, Weinberg operator, seesaw models, low-scale seesaw models, inverse seesaw, right-handed neutrinos, renormalization group, threshold effects, neutrinoless double beta decay
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-35267ISBN: 978-91-7501-057-1 (print)OAI: oai:DiVA.org:kth-35267DiVA: diva2:426447
Presentation
2011-08-26, FB53, KTH, Roslagstullsbacken 21, Stockholm, Sweden, 13:00 (English)
Opponent
Supervisors
Note
QC 20110812Available from: 2011-08-12 Created: 2011-06-23 Last updated: 2011-08-12Bibliographically approved
List of papers
1. Renormalization group running of neutrino parameters in the inverse seesaw model
Open this publication in new window or tab >>Renormalization group running of neutrino parameters in the inverse seesaw model
2010 (English)In: Physical Review D, ISSN 1550-7998, Vol. 81, no 11, 116006- p.Article in journal (Refereed) Published
Abstract [en]

We perform a detailed study of the renormalization group equations in the inverse seesaw model. Especially, we derive compact analytical formulas for the running of the neutrino parameters in the standard model and the minimal supersymmetric standard model, and illustrate that, due to large Yukawa coupling corrections, significant running effects on the leptonic mixing angles can be naturally obtained in the proximity of the electroweak scale, perhaps even within the reach of the LHC. In general, if the mass spectrum of the light neutrinos is nearly degenerate, the running effects are enhanced to experimentally accessible levels, well suitable for the investigation of the underlying dynamics behind the neutrino mass generation and the lepton flavor structure. In addition, the effects of the seesaw thresholds are discussed, and a brief comparison to other seesaw models is carried out.

Place, publisher, year, edition, pages
The American Physical Society, 2010
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-27231 (URN)10.1103/PhysRevD.81.116006 (DOI)000279386200001 ()2-s2.0-77954388448 (Scopus ID)
Funder
Swedish Research Council, 621-2008-4210
Note
QC 20101229Available from: 2011-09-26 Created: 2010-12-09 Last updated: 2013-08-30Bibliographically approved
2. Threshold effects on renormalization group running of neutrino parameters in the low-scale seesaw model
Open this publication in new window or tab >>Threshold effects on renormalization group running of neutrino parameters in the low-scale seesaw model
2011 (English)In: Physics Letters B, ISSN 0370-2693, Vol. 698, no 4, 297-305 p.Article in journal (Refereed) Published
Abstract [en]

We show that, in the low-scale type-I seesaw model, renormalization group running of neutrino parameters may lead to significant modifications of the leptonic mixing angles in view of so-called seesaw threshold effects. Especially, we derive analytical formulas for radiative corrections to neutrino parameters in crossing the different seesaw thresholds, and show that there may exist enhancement factors efficiently boosting the renormalization group running of the leptonic mixing angles. We find that, as a result of the seesaw threshold corrections to the leptonic mixing angles, various flavor symmetric mixing patterns (e.g., bi-maximal and tri-bimaximal mixing patterns) can be easily accommodated at relatively low energy scales, which is well within the reach of running and forthcoming experiments (e.g., the LHC).

Place, publisher, year, edition, pages
Elsevier B.V., 2011
Keyword
Renormalization group equations, Threshold effects, TeV seesaw models
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-33701 (URN)10.1016/j.physletb.2011.03.028 (DOI)000290077000007 ()2-s2.0-79953161892 (Scopus ID)
Funder
Swedish Research Council, 621-2008-4210
Note
QC 20110523Available from: 2011-09-26 Created: 2011-05-16 Last updated: 2013-08-30Bibliographically approved
3. Constraining new physics with a positive or negative signal of neutrino-less double beta decay
Open this publication in new window or tab >>Constraining new physics with a positive or negative signal of neutrino-less double beta decay
2011 (English)In: Journal of High Energy Physics (JHEP), ISSN 1029-8479, E-ISSN 1126-6708, Vol. 2011, no 05, 122- p.Article in journal (Refereed) Published
Abstract [en]

We investigate numerically how accurately one could constrain the strengths of different short-range contributions to neutrino-less double beta decay in effective field theory. Depending on the outcome of near-future experiments yielding information on the neutrino masses, the corresponding bounds or estimates can be stronger or weaker. A particularly interesting case, resulting in strong bounds, would be a positive signal of neutrino-less double beta decay that is consistent with complementary information from neutrino oscillation experiments, kinematical determinations of the neutrino mass, and measurements of the sum of light neutrino masses from cosmological observations. The keys to more robust bounds are improvements of the knowledge of the nuclear physics involved and a better experimental accuracy.

Keyword
Rare Decays, Beyond Standard Model, Neutrino Physics
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-34849 (URN)10.1007/JHEP05(2011)122 (DOI)000291364500054 ()2-s2.0-80053161286 (Scopus ID)
Funder
Swedish Research Council, 621-2008-4210
Note
QC 20110616Available from: 2011-09-26 Created: 2011-06-16 Last updated: 2013-08-30Bibliographically approved

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