57 research outputs found
The Strong CP Problem and Discrete Symmetries
We discuss a possible solution to the strong CP problem which is based on
spontaneous CP violation and discrete symmetries. At the same time we predict
in a simple way the almost right-angled quark unitarity triangle angle () by making the entries of the quark mass matrices either real
or imaginary. To prove the viability of our strategy we present a toy flavour
model for the quark sector.Comment: 10 pages, 1 figure, contribution to the International Conference on
Massive Neutrinos, Singapore, 9 - 13 February 201
GUT predictions for quark and lepton mass ratios
Group theoretical factors from GUT symmetry breaking can lead to predictions
for the ratios of quark and lepton masses at the unification scale. Due to
supersymmetric (SUSY) threshold corrections the viability of such predictions
can depend strongly on the SUSY parameters. We derive possible new predictions
for the GUT scale ratios m_\mu/m_s, y_\tau/y_b and y_t/y_b and compare them
with the experimentally allowed ranges for three common SUSY breaking
scenarios.Comment: Based on a talk given at SUSY 09; 5 pages, 1 figure, 2 table
Neutrino Mass Sum Rules and Symmetries of the Mass Matrix
Neutrino mass sum rules have recently gained again more attention as a
powerful tool to discriminate and test various flavour models in the near
future. A related question which was not yet discussed fully satisfactorily was
the origin of these sum rules and if they are related to any residual or
accidental symmetry. We will address this open issue here systematically and
find previous statements confirmed. Namely, that the sum rules are not related
to any enhanced symmetry of the Lagrangian after family symmetry breaking but
that they are simply the result of a reduction of free parameters due to
skillful model building.Comment: 10 pages, no figures, accepted for publication in European Physical
Journal
Renormalisation Group Corrections to Neutrino Mass Sum Rules
Neutrino mass sum rules are an important class of predictions in flavour
models relating the Majorana phases to the neutrino masses. This leads, for
instance, to enormous restrictions on the effective mass as probed in
experiments on neutrinoless double beta decay. While up to now these sum rules
have in practically all cases been taken to hold exactly, we will go here
beyond that. After a discussion of the types of corrections that could possibly
appear and elucidating on the theory behind neutrino mass sum rules, we
estimate and explicitly compute the impact of radiative corrections, as these
appear in general and thus hold for whole groups of models. We discuss all
neutrino mass sum rules currently present in the literature, which together
have realisations in more than 50 explicit neutrino flavour models. We find
that, while the effect of the renormalisation group running can be visible, the
qualitative features do not change. This finding strongly backs up the solidity
of the predictions derived in the literature, and it thus marks a very
important step in deriving testable and reliable predictions from neutrino
flavour models.Comment: 25 pages, 3 figures, 39 additional plots; version published in JHE
Confronting SUSY SO(10) with updated Lattice and Neutrino Data
We present an updated fit of supersymmetric SO(10) models to quark and lepton
masses and mixing parameters. Including latest results from lattice QCD
determinations of quark masses and neutrino oscillation data, we show that fits
neglecting supersymmetric threshold corrections are strongly disfavoured in our
setup. Only when we include these corrections we find good fit points. We
present -profiles for the threshold parameters, which show that in our
setup the thresholds related to the third generation of fermions exhibit two
rather narrow minima.Comment: 23 pages, 3 figures, and 5 tables; version published in JHE
New Aspects of Flavour Model Building in Supersymmetric Grand Unification
We derive predictions for Yukawa coupling ratios within GUTs generated from
operators with mass dimension four and five. These relations are a
characteristic property of unified flavour models and can reduce the large
number of free parameters related to the flavour sector of the SM. The Yukawa
couplings of the down-type quarks and charged leptons are affected within SUSY
models by tan beta-enhanced threshold corrections. We analyse these corrections
and give simple analytic expressions and numerical estimates for them. The
threshold corrections sensitively depend on the soft SUSY breaking parameters.
Especially, they determine if the affected Yukawa couplings are enhanced or
suppressed. In a first approach, we make some plausible assumptions about the
soft SUSY parameters. In a second, more sophisticated approach we use three
common breaking schemes in which all the soft breaking parameters at the
electroweak scale can be calculated from only a handful of parameters. Within
this approach, we apply various phenomenological constraints on the
supersymmetric parameters and find in this way new viable Yukawa coupling
relations, for example y_mu/y_s = 9/2 or 6 or y_tau/y_b = 3/2 in SU(5).
Furthermore, we study a special class of quark mass matrix textures for small
tan beta where theta_13^u = theta_13^d = 0. We derive sum rules for the quark
mixing parameters and find a simple relation between the two phases delta_12^u
and delta_12^d and the right unitarity triangle angle alpha which suggests a
simple phase structure for the quark mass matrices. To complement the
aforementioned considerations, we give two explicit examples in an SU(5)
context, one for large and one for small tan beta which implement the Yukawa
coupling relations mentioned before. The models have interesting
phenomenological consequences like, for example, quasi-degenerate neutrino
masses in the case of small tan beta.Comment: PhD thesis, 205 pages, 25 figures (approx. 6 MB
GUT predictions for quark-lepton Yukawa coupling ratios with messenger masses from non-singlets
We propose new predictions from grand unified theories (GUTs) [applicable to both supersymmetric (SUSY) and non-SUSY models] for the ratios of quark and lepton Yukawa couplings. These new predictions arise from splitting the masses of the messenger fields for the GUT-scale Yukawa operators by Clebsch-Gordan factors from GUT symmetry breaking. This has the effect that these factors enter inversely in the predicted quark-lepton Yukawa coupling ratios, leading to new possible GUT predictions. We systematically construct the new predictions that can be realized in this way in SU(5) GUTs and Pati-Salam unified theories and discuss model building applications
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