201 research outputs found
Matter Inflation in Supergravity
No full textAntusch, Stefan. (2011). Matter Inflation in Supergravity. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/118929
Sequential dominance
No full textWe review the mechanism of sequential right-handed neutrino dominance proposed in the framework of the type I see-saw mechanism to account for bi-large neutrino mixing and a neutrino mass hierarchy in a natural way. We discuss how sequential dominance (SD) may also be applied to the right-handed charged leptons, which alternatively allows for bi-large lepton mixing from the charged lepton sector. We review how such SD models may be upgraded to include type II see-saw contributions, resulting in a partially degenerate neutrino mass spectrum with the bi-large lepton mixing arising from SD. We also summarize the model-building applications and the phenomenological implications of SD
From hierarchical to partially degenerate neutrinos via type II upgrade of type I see-saw models
No full textWe propose a type II upgrade of type I see-saw models leading to new classes of models where partially degenerate neutrinos are as natural as hierarchical ones. The additional type II contribution to the neutrino mass matrix, which determines the neutrino mass scale, is forced to be proportional to the unit matrix by a SO(3) flavour symmetry. The type I see-saw part of the neutrino mass matrix, which controls the mass squared differences and mixing angles, may be governed by sequential right-handed neutrino dominance and a natural alignment for the SO(3)-breaking vacuum. We focus on classes of models with bi-large mixing originating from the neutrino mass matrix although we also briefly discuss other classes of models where large mixing stems from the charged lepton mass matrix. We study renormalization group corrections to the neutrino mass squared differences and mixings and find that the low energy values do not depend sensitively on the high energy values for partially degenerate neutrinos with a mass scale up to about 0.15 eV. Our scenario predicts the effective mass for neutrinoless double beta decay to be approximately equal to the neutrino mass scale and therefore neutrinoless double beta decay will be observable if the neutrino mass spectrum is partially degenerate. We also find that all observable CP phases become small as the neutrino mass scale increases
Leptogenesis in unified theories with type II see-saw
No full textIn some classes of flavour models based on unified theories with a type I see-saw mechanism, the prediction for the mass of the lightest right-handed neutrino is in conflict with the lower bound from the requirement of successful thermal leptogenesis. We investigate how lifting the absolute neutrino mass scale by adding a type II see-saw contribution proportional to the unit matrix can solve this problem. Generically, lifting the neutrino mass scale increases the prediction for the mass of the lightest right-handed neutrino while the decay asymmetry is enhanced and washout effects are reduced, relaxing the lower bound on the mass of the lightest right-handed neutrino from thermal leptogenesis. For instance in classes of unified theories where the lightest right-handed neutrino dominates the type I see-saw contribution, we find that thermal leptogenesis becomes possible if the neutrino mass scale is larger than about 0.15 eV, making this scenario testable by neutrinoless double beta decay experiments in the near future
A fuller flavour treatment of N_2-dominated leptogenesis
No full textWe discuss N_2-dominated leptogenesis in the presence of flavour dependent effects that have hitherto been neglected, in particular the off-diagonal entries of the flavour coupling matrix that connects the total flavour asymmetries, distributed in different particle species, to the lepton and Higgs doublet asymmetries. We derive analytical formulae for the final asymmetry including the flavour coupling at the N_2-decay stage as well as at the stage of washout by the lightest right-handed neutrino N_1. We point out that in general part of the electron and muon asymmetries can completely escape the wash-out at the production and a total B-L asymmetry can be generated by the lightest RH neutrino wash-out yielding so called phantom leptogenesis. Taking of all these new effects into account can enhance the final asymmetry produced by the decays of the next-to-lightest RH neutrinos by orders of magnitude, opening up new interesting possibilities for N_2-dominated thermal eptogenesis. We illustrate these effects for two models which describe realistic neutrino masses and mixing based on sequential dominance
Spontaneous CP violation in with Constrained Sequential Dominance 2
No full textWe revisit a two right-handed neutrino model with two texture zeros, namely an indirect model based on A4 with the recently proposed new type of constrained sequential dominance (CSD2), involving vacuum alignments along the (0,1,?1)T and (1,0,2)T directions in flavor space, which are proportional to the neutrino Dirac mass matrix columns. In this paper we construct a renormalizable and unified indirect A4×SU(5) model along these lines and show that, with spontaneous CP violation and a suitable vacuum alignment of the phases, the charged lepton corrections lead to a reactor angle in good agreement with results from Daya Bay and RENO. The model predicts a right-angled unitarity triangle in the quark sector and a Dirac CP violating oscillation phase in the lepton sector of ??130°, while providing a good fit to all quark and lepton masses and mixing angle
Third family corrections to tri-bimaximal lepton mixing and a new sum rule
No full textWe investigate the theoretical stability of the predictions of tri-bimaximal neutrino mixing with respect to third family wave-function corrections. Such third family wave-function corrections can arise from either the canonical normalisation of the kinetic terms or renormalisation group running effects. At leading order both sorts of corrections can be subsumed into a single universal parameter. For hierarchical neutrinos, this leads to a new testable lepton mixing sum rule s = r cos ? + 2/3a (where s,r,a describe the deviations of solar, reactor and atmospheric mixing angles from their tri-bimaximal values, and ? is the observable Dirac CP phase) which is stable under all leading order third family wave-function corrections, as well as Cabibbo-like charged lepton mixing effects
Solving the SUSY flavour and CP problems with SU(3) family symmetry
No full textWe show how the SUSY flavour and CP problems can be solved using gauged SU(3) family symmetry previously introduced to describe quark and lepton masses and mixings, in particular neutrino tri-bimaximal mixing via constrained sequential dominance. The Yukawa and soft trilinear and scalar mass squared matrices and kinetic terms are expanded in powers of the flavons used to spontaneously break the SU(3) family symmetry, and the canonically normalized versions of these matrices are constructed. The soft mass matrices are then expressed in the Super-CKM basis, and the leading order mass insertion parameters are calculated, and are shown to satisfy the experimental constraints from flavour changing neutral current processes. Assuming that CP is spontaneously broken by the flavons, the next-to-leading order effects responsible for CP violation are then estimated, and the predictions for electric dipole moments are shown to be an order of magnitude more suppressed than those predicted from the constrained minimal supersymmetric standard model (CMSSM), and may be further suppressed if the high energy trilinear soft parameter is assumed to be relatively small. We also predict that, unlike in the CMSSM, ?K'/?K may be dominated by the SUSY operator O8. We also discuss the additional constraints from unification, which can lead to further predictions for flavour changing in our scheme
Third family corrections to quark and lepton mixing in SUSY models with non-abelian family symmetry
No full textWe re-analyse the effect of corrections from canonical normalisation of kinetic terms on the quark and lepton mixing angles. This type of corrections emerges, for example, from effective higher-dimensional Kähler potential operators in the context of locally supersymmetric models of flavour. In contrast to previous studies we find that the necessary procedure of redefining the fields in order to restore canonically normalised kinetic terms, i.e. canonical normalisation, can lead to significant corrections to the fermion mixing angles (as determined from the superpotential). Such potentially large effects are characteristic of flavour models based on non-Abelian family symmetries, where some of the possible Kähler potential (and superpotential) operators, in particular those associated with the third family, are only mildly suppressed. We investigate under which conditions the messenger sector of such flavour models generates such Kähler potential operators for which the canonical normalisation effects are sizeable, and under which conditions these operators may be absent and canonical normalisation effects are small. As explicit examples for potentially relevant CN effects, we will discuss the corrections to the CKM matrix element |Vcb| as well as corrections to tri-bimaximal neutrino mixing
Predicting the flavour and SUSY flavour structure from grand unified theories
No full textGrand Unified Theories (GUTs) offer an attractive framework for flavour models, since they feature relations between quarks and leptons. Combining them with Supersymmetry (SUSY) and flavour symmetries, we derive predictions for the flavour and SUSY flavour structure from various GUT models and discuss how the double missing partner mechanism (DMPM) solution to the doublet-triplet splitting problem can be combined with predictions for GUT scale quark-lepton Yukawa coupling relations.
We construct two predictive SUSY SU(5) GUT models with an A4 flavour symmetry, that feature realistic quark-lepton Yukawa coupling ratios and mixing angle relations. These GUT scale predictions arise after GUT symmetry breaking from a novel combination of group theoretical Clebsch-Gordan factors, and we carefully construct additional shaping symmetries and renormalisable messenger sectors to protect the models' predictions from dangerous corrections. The major difference between both models are their respective predictions of a normal and inverse neutrino mass ordering. We perform Markov Chain Monte Carlo analyses, fit to experimental data, and discuss how the models can be tested by present and future experiments.
To combine predictive GUT scale quark-lepton Yukawa coupling ratios with the DMPM in SUSY SU(5), we introduce a second GUT breaking Higgs field in the adjoint representation. Two explicit flavour models with different predictions for the GUT scale Yukawa sector are presented, including shaping symmetries and renormalisable messenger sectors, and combined with the DMPM. We calculate the effective masses of the colour triplets mediating proton decay and find that they can be made sufficiently heavy.
In SUSY theories, the one-loop SUSY threshold corrections are of particular importance in investigating GUT scale quark-lepton mass relations and thus link a given GUT flavour model to the sparticle spectrum. We calculate the one-loop SUSY threshold corrections of the full MSSM Yukawa coupling matrices in the electroweak-unbroken phase and introduce a new software tool SusyTC as a major extension to the Mathematica package REAP. Finally we find predictions for the CMSSM parameters and sparticle masses from the GUT scale Yukawa coupling ratios used in the flavour models of this thesis
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