35 research outputs found
New GUT predictions for quark and lepton mass ratios confronted with phenomenology
Group theoretical factors from GUT symmetry breaking can lead to predictions
for the ratios of quark and lepton masses (or Yukawa couplings) at the
unification scale. Due to supersymmetric (SUSY) threshold corrections the
viability of such predictions can depend strongly on the SUSY parameters. For
three common minimal SUSY breaking scenarios with anomaly, gauge and gravity
mediation we investigate which GUT scale ratios , ,
and are allowed when phenomenological constraints from
electroweak precision observables, physics, , mass-limits on
sparticles from direct searches as well as, optionally, constraints from the
observed dark matter density are taken into account. We derive possible new
predictions for the GUT scale mass ratios and compare them with the
phenomenologically allowed ranges. We find that new GUT scale predictions such
as or 6 and or 2 are often favoured
compared to the ubiquitous relations or . They
are viable for characteristic SUSY scenarios, testable at the CERN LHC and
future colliders.Comment: 33 pages, 5 figures; references added; version to appear in Phys.
Rev.
Higgs couplings in the MSSM at large tan(beta)
We consider tan(beta)-enhanced quantum effects in the minimal supersymmetric
standard model (MSSM) including those from the Higgs sector. To this end, we
match the MSSM to an effective two-Higgs doublet model (2HDM), assuming that
all SUSY particles are heavy, and calculate the coefficients of the operators
that vanish or are suppressed in the MSSM at tree-level. Our result clarifies
the dependence of the large-tan(beta) resummation on the renormalization
convention for tan(beta), and provides analytic expressions for the Yukawa and
trilinear Higgs interactions. The numerical effect is analyzed by means of a
parameter scan, and we find that the Higgs-sector effects, where present, are
typically larger than those from the "wrong-Higgs" Yukawa couplings in the
2HDM.Comment: 27 pages, LaTe
An SU(5)×A5 golden ratio flavour model
In this paper we study an SU(5)×A5 flavour model which exhibits a neutrino mass sum rule and golden ratio mixing in the neutrino sector which is corrected from the charged lepton Yukawa couplings. We give the full renormalisable superpotential for the model which breaks SU(5) and A5 after integrating out heavy messenger fields and minimising the scalar potential. The mass sum rule allows for both mass orderings but we will show that inverted ordering is not valid in this setup. For normal ordering we find the lightest neutrino to have a mass of about 10-50 meV, and all leptonic mixing angles in agreement with experiment
Leptogenesis in an SU(5)×A5 golden ratio flavour model
In this paper we discuss a minor modification of a previous SU(5)×A5 flavour model which exhibits at leading order golden ratio mixing and sum rules for the heavy and the light neutrino masses. Although this model could predict all mixing angles well it fails in generating a sufficient large baryon asymmetry via the leptogenesis mechanism. We repair this deficit here, discuss model building aspects and give analytical estimates for the generated baryon asymmetry before we perform a numerical parameter scan. Our setup has only a few parameters in the lepton sector. This leads to specific constraints and correlations between the neutrino observables. For instance, we find that in the model considered only the neutrino mass spectrum with normal mass ordering and values of the lightest neutrino mass in the interval 10–18 meV are compatible with the current data on the neutrino oscillation parameters. With the introduction of only one NLO operator, the model can accommodate successfully simultaneously even at 1 σ level the current data on neutrino masses, on neutrino mixing and the observed value of the baryon asymmetry
Right unitarity triangles and tri-bimaximal mixing from discrete symmetries and unification
We propose new classes of models which predict both tri-bimaximal lepton
mixing and a right-angled Cabibbo-Kobayashi-Maskawa (CKM) unitarity triangle,
alpha approximately 90 degrees. The ingredients of the models include a
supersymmetric (SUSY) unified gauge group such as SU(5), a discrete family
symmetry such as A4 or S4, a shaping symmetry including products of Z2 and Z4
groups as well as spontaneous CP violation. We show how the vacuum alignment in
such models allows a simple explanation of alpha approximately 90 degrees by a
combination of purely real or purely imaginary vacuum expectation values (vevs)
of the flavons responsible for family symmetry breaking. This leads to quark
mass matrices with 1-3 texture zeros that satisfy the phase sum rule and lepton
mass matrices that satisfy the lepton mixing sum rule together with a new
prediction that the leptonic CP violating oscillation phase is close to either
0, 90, 180, or 270 degrees depending on the model, with neutrino masses being
purely real (no complex Majorana phases). This leads to the possibility of
having right-angled unitarity triangles in both the quark and lepton sectors.Comment: 29 pages, 4 figures, version to be published in NP
Proceedings of the 2nd Workshop on Flavor Symmetries and Consequences in Accelerators and Cosmology (FLASY12)
These are the proceedings of the 2nd Workshop on Flavor Symmetries and
Consequences in Accelerators and Cosmology, held 30 June 2012 - 4 July 2012,
Dortmund, Germany.Comment: Order 400 pages, several figures including the group picture v2:
corrected author list and contributio
Phenomenology of Minimal Unified Tree Level Gauge Mediation at the LHC
We study the collider phenomenology of the minimal unified version of the supersymmetry breaking scheme called Tree-level Gauge Mediation. We identify a peculiar source of gaugino mass non-universality related to the necessary SU(5)-breaking in the light fermion mass ratios and a gaugino mass sum rule at the GUT scale, 3 M_2 + 2 M_3 = 5 M_1, which represents a smoking gun of this scenario, together with the known tree-level sfermion mass ratio \tilde m_{d^c,l} = \sqrt{2} \tilde m_{q,u^c,e^c}. The boundary conditions of the soft SUSY breaking terms can be parameterised in terms of six relevant parameters only (plus the sign of the \mu-parameter). We analyze the parameter space and define three benchmark points, corresponding to the three possible NLSPs, a bino- or wino-like neutralino or the stau. The LSP is the gravitino as in gauge mediation. For these benchmark points we show possible signatures at the LHC focusing on the Razor variable. We also comment on the Higgs mass
Renormalisation group corrections to neutrino mixing sum rules
Neutrino mixing sum rules are common to a large class of models based on the
(discrete) symmetry approach to lepton flavour. In this approach the neutrino
mixing matrix is assumed to have an underlying approximate symmetry form
\tildeU_\nu, which is dictated by, or associated with, the employed
(discrete) symmetry. In such a setup the cosine of the Dirac CP-violating phase
can be related to the three neutrino mixing angles in terms of a sum
rule which depends on the symmetry form of \tildeU_\nu. We consider five
extensively discussed possible symmetry forms of \tildeU_\nu: i)
bimaximal (BM) and ii) tri-bimaximal (TBM) forms, the forms corresponding to
iii) golden ratio type A (GRA) mixing, iv) golden ratio type B (GRB) mixing,
and v) hexagonal (HG) mixing. For each of these forms we investigate the
renormalisation group corrections to the sum rule predictions for in
the cases of neutrino Majorana mass term generated by the Weinberg (dimension
5) operator added to i) the Standard Model, and ii) the minimal SUSY extension
of the Standard Model
Generalised geometrical CP violation in a T' lepton flavour model
We analyse the interplay of generalised CP transformations and the non-Abelian discrete group T \u2032 and use the semi-direct product G f = T \u2032 caH CP, as family symmetry acting in the lepton sector. The family symmetry is shown to be spontaneously broken in a geometrical manner. In the resulting flavour model, naturally small Majorana neutrino masses for the light active neutrinos are obtained through the type I see-saw mechanism. The known masses of the charged leptons, lepton mixing angles and the two neutrino mass squared differences are reproduced by the model with a good accuracy. The model allows for two neutrino mass spectra with normal ordering (NO) and one with inverted ordering (IO). For each of the three spectra the absolute scale of neutrino masses is predicted with relatively small uncertainty. The value of the Dirac CP violation (CPV) phase \u3b4 in the lepton mixing matrix is predicted to be \u3b4 = \u3c0/2 or 3\u3c0/2. Thus, the CP violating effects in neutrino oscillations are predicted to be maximal (given the values of the neutrino mixing angles) and experimentally observable. We present also predictions for the sum of the neutrino masses, for the Majorana CPV phases and for the effective Majorana mass in neutrinoless double beta decay. The predictions of the model can be tested in a variety of ongoing and future planned neutrino experiments