32 research outputs found
\theta^PMNS_13 = \theta_C / \sqrt2 from GUTs
The recent observations of the leptonic mixing angle \theta^PMNS_13 are
consistent with \theta^PMNS_13 = \theta_C / \sqrt2 (with \theta_C being the
Cabibbo angle \theta^CKM_12). We discuss how this relation can emerge in Grand
Unified Theories (GUTs) via charged lepton corrections. The key ingredient is
that in GUTs the down-type quark Yukawa matrix and the charged lepton Yukawa
matrix are generated from the same set of GUT operators, which implies that the
resulting entries are linked and differ only by group theoretical Clebsch
factors. This allows a link \theta^e_12 = \theta_C to be established, which can
induce \theta^PMNS_13 = \theta_C / \sqrt2 provided that the 1-3 mixing in the
neutrino mass matrix is much smaller than \theta_C. We find simple conditions
under which \theta^PMNS_13 = \theta_C / \sqrt2 can arise via this link in SU(5)
GUTs and Pati-Salam models. We also discuss possible corrections to this
relation. Using lepton mixing sum rules different neutrino mixing patterns can
be distinguished by their predictions for the Dirac CP phase \delta^PMNS.Comment: v3: 18 pages, section on corrections to exact relation adde
symmetry at colliders and in the universe
Two puzzling facts of our time are the observed patterns in the fermion
masses and mixings and the existence of non-baryonic dark matter, which are
both often associated with extensions of the Standard Model at higher energy
scales. In this paper, we consider a solution to these two problems with the
flavour symmetry , in a model which has been shown before to explain large leptonic
mixings with a specific texture. The model contains 3 generations of
-doublet scalar fields, arranged as an -triplet, that
spontaneously break the electroweak symmetry, and a "dark sector" of -odd fields, containing one Majorana neutrino and an -triplet -doublet scalar field, the lightest of which provides a
candidate for dark matter.
Concerning the -even scalar fields, compared to the Standard
Model, we predict additional fields with masses at the electroweak scale. We
therefore investigate present phenomenological constraints from lepton flavour
violation experiments, obtaining a lower bound on the extra scalar masses of
140 GeV. Furthermore we consider the oblique parameters, Higgs boson decay
properties and possible flavour violating signals at the LHC.
Concerning the "dark sector", we study bounds from dark matter search
experiments and identify the parameter space of the dark matter candidate that
is compatible with the observed relic density. We find two allowed mass ranges
for the dark matter within which the experimental constraints can be
accommodated: the low-mass range is from 47 GeV to 74 GeV and the high-mass
range is from 600 GeV and 3.6 TeV.Comment: v2, to be published in JHE
Naturalness and GUT Scale Yukawa Coupling Ratios in the CMSSM
We analyse the fine-tuning in the Constrained Minimal Supersymmetric Standard
Model (CMSSM) in the light of the present and expected ATLAS and CMS SUSY
searches. Even with 10/fb of data and no discovery of SUSY valid regions might
remain with fine-tuning less than 20. Moreover we investigate the fine-tuning
price of GUT scale Yukawa coupling relations. Considering a 2
constraint for and fine-tuning less than 30 yields an allowed range
of , which points towards the alternative GUT
prediction . Relaxing the constraint to 5
extends the possible region to [1.02,1.70], allowing for approximate
Yukawa coupling unification.Comment: 13 pages, 3 figures; version published in PR
Large neutrino mixing angle \theta_{13}^{MNS} and quark-lepton mass ratios in unified flavour models
We analyse how a large value of the leptonic mixing angle \theta_{13}^{MNS}
can be generated via charged lepton corrections in unified flavour models,
using novel combinations of Clebsch-Gordan factors for obtaining viable
quark-lepton mass ratios for the first two families. We discuss how these
Clebsch-Gordan factors affect the relations between down-type quark mixing and
charged lepton mixing in SU(5) GUTs and Pati-Salam unified models and calculate
the resulting possible predictions for \theta_{13}^{MNS} for models with
\theta_{13}^\nu, \theta_{13}^e << \theta_{12}^e. While symmetric mass matrices
with zero (1,1)-elements always lead to comparatively small \theta_{13}^{MNS}
\approx 2.8 degrees, we find novel combinations of Clebsch-Gordan factors for
non-symmetric mass matrices which can yield \theta_{13}^{MNS} \approx 5.1
degrees, 6.1 degrees, 7.6 degrees or 10.1 degrees, as favoured by the current
experimental hints for large \theta_{13}^{MNS}. We discuss applications to
classes of models with underlying tri-bimaximal or bimaximal mixing in the
neutrino sector.Comment: 8 pages, version published in PR
Towards predictive flavour models in SUSY SU(5) GUTs with doublet-triplet splitting
We discuss how the double missing partner mechanism solution to the
doublet-triplet splitting problem in four-dimensional supersymmetric SU(5)
Grand Unified Theories (GUTs) can be combined with predictive models for the
quark-lepton Yukawa coupling ratios at the GUT scale. It is argued that towards
this goal a second SU(5) breaking Higgs field in the adjoint representation is
very useful and we discuss all possible renormalizable superpotentials with two
adjoint Higgs fields and calculate the constraints on the GUT scale and
effective triplet mass from a two-loop gauge coupling unification analysis. Two
explicit flavour models with different predictions for the GUT scale Yukawa
sector are presented, including shaping symmetries and a renormalizable
messenger sector. Towards calculating the rates for proton decay induced by the
exchange of colour triplets, the required Clebsch-Gordan coefficients for their
couplings are calculated for the possible dimension five and six operators.
They are provided in detailed tables in the appendix, together with additional
helpful material for GUT flavour model building.Comment: 47 pages, 9 figures; version published in JHE
A flavour GUT model with theta_13^PMNS = theta_C / sqrt(2)
We propose a supersymmetric SU(5) GUT model with an A_4 family symmetry -
including a full flavon- and messenger sector - which realises the relation
theta_13^PMNS \simeq theta_C / sqrt(2). The neutrino sector features
tri-bimaximal mixing, and theta_13^PMNS \simeq theta_C / sqrt(2) emerges from
the charged lepton contribution to the PMNS matrix, which in turn is linked to
quark mixing via specific GUT relations. These GUT relations arise after GUT
symmetry breaking from a novel combination of group theoretical Clebsch-Gordan
factors, which in addition to large theta_13^PMNS lead to promising quark
lepton mass ratios for all generations of quarks and leptons and to m_s / m_d =
18.95_(-0.24)^(+0.33), in excellent agreement with experimental results. The
model also features spontaneous CP violation, with all quark and lepton CP
phases determined from family symmetry breaking. We perform a full Markov Chain
Monte Carlo fit to the available quark and lepton data, and discuss how the
model can be tested by present and future experiments.Comment: 21 pages, version accepted for publication in Nuclear Physics
Temporary collapse of the Daphnia population in turbid and ultra-oligotrophic Lake Brienz
Abstract.: The cyclical parthenogen Daphnia is a key species in aquatic food webs. Its abundance is influenced by environmental factors like food quantity and quality, predation, diseases, temperature and washout by discharge. In ultra-oligotrophic Lake Brienz (Switzerland), which is turbid from suspended glacial material, Daphnia density has continuously decreased since the 1990 s. In spring and summer 1999, during and after a severe flood, Daphnia density was below detection level, but the population recovered the following year. Simultaneously, a drastic two-year decline occurred in the yield of whitefish (Coregonus sp.), which mainly feed on Daphnia. Several hypotheses were tested to explain the collapse of the Daphnia population: a negative effect of the suspended particles, a covering of the diapausing eggs by sediment, and a combined washout/temperature effect. A direct negative effect of the particles and covering of diapausing eggs could be excluded. According to model calculations, the spring growth of the Daphnia population could not compensate the washout losses, as it was limited by poor food conditions due to re-oligotrophication and reduced by extraordinarily low water temperatures. Moreover, ephippia abundance analysed from sediment cores was consistent with the process of eutrophication and re-oligotrophication and indicated that daphnids did not persist in the lake in the period before eutrophication (until 1955). Like most peri-alpine lakes in Europe, Lake Brienz has returned to its natural ultra-oligotrophic state and is now unable to support a large Daphnia population and fishing yiel
Naturalness and GUT Scale Yukawa Coupling Ratios in the CMSSM
We analyse the fine-tuning in the Constrained Minimal Supersymmetric Standard
Model (CMSSM) in the light of the present and expected ATLAS and CMS SUSY
searches. Even with 10/fb of data and no discovery of SUSY valid regions might
remain with fine-tuning less than 20. Moreover we investigate the fine-tuning
price of GUT scale Yukawa coupling relations. Considering a 2
constraint for and fine-tuning less than 30 yields an allowed range
of , which points towards the alternative GUT
prediction . Relaxing the constraint to 5
extends the possible region to [1.02,1.70], allowing for approximate
Yukawa coupling unification.Comment: 13 pages, 3 figures; version published in PR
From Flavour to SUSY Flavour Models
If supersymmetry (SUSY) will be discovered, successful models of flavour not
only have to provide an explanation of the flavour structure of the Standard
Model fermions, but also of the flavour structure of their scalar
superpartners. We discuss aspects of such "SUSY flavour" models, towards
predicting both flavour structures, in the context of supergravity (SUGRA). We
point out the importance of carefully taking into account SUSY-specific
effects, such as 1-loop SUSY threshold corrections and canonical normalization,
when fitting the model to the data for fermion masses and mixings. This
entangles the flavour model with the SUSY parameters and leads to interesting
predictions for the sparticle spectrum. We demonstrate these effects by
analyzing an example class of flavour models in the framework of an SU(5) Grand
Unified Theory with a family symmetry with real triplet representations. For
flavour violation through the SUSY soft breaking terms, the class of models
realizes a scheme we refer to as "Trilinear Dominance", where flavour violation
effects are dominantly induced by the trilinear terms.Comment: 44 pages, 10 figures, version published in Nuclear Physics