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Models in Neutrino Physics: Numerical and Statistical Studies
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.ORCID iD: 0000-0002-7142-2783
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The standard model of particle physics can excellently describe the vast majorityof data of particle physics experiments. However, in its simplest form, it cannot account for the fact that the neutrinos are massive particles and lepton flavorsmixed, as required by the observation of neutrino oscillations. Hence, the standardmodel must be extended in order to account for these observations, opening up thepossibility to explore new and interesting physical phenomena.

There are numerous models proposed to accommodate massive neutrinos. Thesimplest of these are able to describe the observations using only a small numberof effective parameters. Furthermore, neutrinos are the only known existing particleswhich have the potential of being their own antiparticles, a possibility that isactively being investigated through experiments on neutrinoless double beta decay.In this thesis, we analyse these simple models using Bayesian inference and constraintsfrom neutrino-related experiments, and we also investigate the potential offuture experiments on neutrinoless double beta decay to probe other kinds of newphysics.

In addition, more elaborate theoretical models of neutrino masses have beenproposed, with the seesaw models being a particularly popular group of models inwhich new heavy particles generate neutrino masses. We study low-scale seesawmodels, in particular the resulting energy-scale dependence of the neutrino parameters,which incorporate new particles with masses within the reach of current andfuture experiments, such as the LHC.

Abstract [sv]

Standardmodellen för partikelfysik beskriver den stora majoriteten data från partikelfysikexperimentutmärkt. Den kan emellertid inte i sin enklaste form beskrivadet faktum att neutriner är massiva partiklar och leptonsmakerna är blandande,vilket krävs enligt observationerna av neutrinooscillationer. Därför måste standardmodellenutökas för att ta hänsyn till detta, vilket öppnar upp möjligheten att utforska nya och intressanta fysikaliska fenomen.

Det finns många föreslagna modeller för massiva neutriner. De enklaste av dessakan beskriva observationerna med endast ett fåtal effektiva parametrar. Dessutom är neutriner de enda kända befintliga partiklar som har potentialen att vara sinaegna antipartiklar, en möjlighet som aktivt undersöks genom experiment på neutrinolöst dubbelt betasönderfall. I denna avhandling analyserar vi dessa enkla modellermed Bayesisk inferens och begränsningar från neutrinorelaterade experiment och undersöker även potentialen för framtida experiment på neutrinolöst dubbelt betasönderfall att bergänsa andra typer av ny fysik.

Även mer avancerade teoretiska modeller för neutrinomassor har föreslagits, med seesawmodeller som en särskilt populär grupp av modeller där nya tunga partiklargenererar neutrinomassor. Vi studerar seesawmodeller vid låga energier, i synnerhetneutrinoparametrarnas resulterande energiberoende, vilka inkluderar nya partiklarmed massor inom räckh°all för nuvarande och framtida experiment såsom LHC.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , xii, 96 p.
Series
Trita-FYS, ISSN 0280-316X ; 2013:50
Keyword [en]
Neutrino mass, lepton mixing, Majorana neutrinos, neutrino oscillations, neutrinoless double beta decay, statistical methods, Bayesian inference, model selection, effective field theory, Weinberg operator, seesaw models, inverse seesaw, right-handed neutrinos, renormalization group, threshold effects.
Keyword [sv]
Neutrinomassor, leptonblandning, Majorananeutriner, neutrinooscillationer, neutrinol¨ost dubbelt betas¨onderfall, statistiska metoder, Bayesisk inferens, modellval, effektiv f¨altteori, Weinbergoperator, seesawmodeller, invers seesaw, högerhänta neutriner, renormeringsgrupp, tröskeleffekter.
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-127409ISBN: 978-91-7501-854-6 (print)OAI: oai:DiVA.org:kth-127409DiVA: diva2:644028
Public defence
2013-09-13, FB54, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130830

Available from: 2013-08-30 Created: 2013-08-29 Last updated: 2013-08-30Bibliographically 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, E-ISSN 1873-2445, 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: 2017-12-11Bibliographically 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 1126-6708, E-ISSN 1029-8479, 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: 2017-12-11Bibliographically approved
4. Bayesian evidence for non-zero theta(13) and CP-violation in neutrino oscillations
Open this publication in new window or tab >>Bayesian evidence for non-zero theta(13) and CP-violation in neutrino oscillations
2012 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2012, no 8, 163- p.Article in journal (Refereed) Published
Abstract [en]

We present the Bayesian method for evaluating the evidence for a non-zero value of the leptonic mixing angle theta(13) and CP-violation in neutrino oscillation experiments. This is an application of the well-established method of Bayesian model selection, of which we give a concise and pedagogical overview. When comparing the hypothesis theta(13) = 0 with hypotheses where theta(13) > 0 using global data but excluding the recent reactor measurements, we obtain only a weak preference for a non-zero theta(13), even though the significance is over 3 sigma. We then add the reactor measurements one by one and show how the evidence for theta(13) > 0 quickly increases. When including the DOUBLE CHOOZ, DAYA BAY, and RENO data, the evidence becomes overwhelming with a posterior probability of the hypothesis theta(13) = 0 below 10(-11). Owing to the small amount of information on the CP-phase delta, very similar evidences are obtained for the CP-conserving and CP-violating hypotheses. Hence, there is, not unexpectedly, neither evidence for nor against leptonic CP-violation. However, when future experiments aiming to search for CP-violation have started taking data, this question will be of great importance and the method described here can be used as an important complement to standard analyses.

Keyword
Neutrino physics, Statistical methods
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-103652 (URN)10.1007/JHEP08(2012)163 (DOI)000309883200006 ()2-s2.0-84865742698 (Scopus ID)
Note

QC 20121018

Available from: 2012-10-18 Created: 2012-10-17 Last updated: 2017-12-07Bibliographically approved
5. Combining and comparing neutrinoless double beta decay experiments using different nuclei
Open this publication in new window or tab >>Combining and comparing neutrinoless double beta decay experiments using different nuclei
2013 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, 093- p.Article in journal (Refereed) Published
Abstract [en]

We perform a global fit of the most relevant neutrinoless double beta decay experiments within the standard model with massive Majorana neutrinos. Using Bayesian inference makes it possible to take into account the theoretical uncertainties on the nuclear matrix elements in a fully consistent way. First, we analyze the data used to claim the observation of neutrinoless double beta decay in Ge-76, and find strong evidence (according to Jeffrey's scale) for a peak in the spectrum and moderate evidence for that the peak is actually close to the energy expected for the neutrinoless decay. We also find a significantly larger statistical error than the original analysis, which we include in the comparison with other data. Then, we statistically test the consistency between this claim with that of recent measurements using Xe-136. We find that the two data sets are about 40 to 80 times more probable under the assumption that they are inconsistent, depending on the nuclear matrix element uncertainties and the prior on the smallest neutrino mass. Hence, there is moderate to strong evidence of incompatibility, and for equal prior probabilities the posterior probability of compatibility is between 1.3% and 2.5%. If one, despite such evidence for incompatibility, combines the two data sets, we find that the total evidence of neutrinoless double beta decay is negligible. If one ignores the claim, there is weak evidence against the existence of the decay. We also perform approximate frequentist tests of compatibility for fixed ratios of the nuclear matrix elements, as well as of the no signal hypothesis. Generalization to other sets of experiments as well as other mechanisms mediating the decay is possible.

Keyword
Rare Decays, Statistical Methods, Neutrino Physics
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-121132 (URN)10.1007/JHEP02(2013)093 (DOI)000316273700016 ()2-s2.0-84875861465 (Scopus ID)
Note

QC 20130419

Available from: 2013-04-19 Created: 2013-04-19 Last updated: 2017-12-06Bibliographically approved

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