2,875 research outputs found

### Vacuum Alignment in SUSY A4 Models

In this note we discuss the vacuum alignment in supersymmetric models with
spontaneously broken flavour symmetries in the presence of soft supersymmetry
(SUSY) breaking terms. We show that the inclusion of soft SUSY breaking terms
can give rise to non-vanishing vacuum expectation values (VEVs) for the
auxiliary components of the flavon fields. These non-zero VEVs can have an
important impact on the phenomenology of this class of models, since they can
induce an additional flavour violating contribution to the sfermion soft mass
matrix of right-left (RL) type. We carry out an explicit computation in a class
of SUSY A4 models predicting tri-bimaximal mixing in the lepton sector. The
flavour symmetry breaking sector is described in terms of flavon and driving
supermultiplets. We find non-vanishing VEVs for the auxiliary components of the
flavon fields and for the scalar components of the driving fields which are of
order m_{SUSY} x and m_{SUSY}, respectively. Thereby, m_{SUSY} is the
generic soft SUSY breaking scale which is expected to be around 1 TeV and
is the VEV of scalar components of the flavon fields. Another effect of these
VEVs can be the generation of a mu term.Comment: 23 pages; added a new section on the relation to Supergravity;
version accepted for publication in JHE

### The Golden Ratio Prediction for the Solar Angle from a Natural Model with A5 Flavour Symmetry

We formulate a consistent model predicting, in the leading order
approximation, maximal atmospheric mixing angle, vanishing reactor angle and
tan {\theta}_12 = 1/{\phi} where {\phi} is the Golden Ratio. The model is based
on the flavour symmetry A5 \times Z5 \times Z3, spontaneously broken by a set
of flavon fields. By minimizing the scalar potential of the theory up to the
next-to-leading order in the symmetry breaking parameter, we demonstrate that
this mixing pattern is naturally achieved in a finite portion of the parameter
space, through the vacuum alignment of the flavon fields. The leading order
approximation is stable against higher-order corrections. We also compare our
construction to other models based on discrete symmetry groups.Comment: 28 pages, 2 figures. Minor changes, references added. Corrected typos
in Appendix A. Version appeared on JHE

### Decaying Dark Matter in the Supersymmetric Standard Model with Freeze-in and Seesaw mechanims

Inspired by the decaying dark matter (DM) which can explain cosmic ray
anomalies naturally, we consider the supersymmetric Standard Model with three
right-handed neutrinos (RHNs) and R-parity, and introduce a TeV-scale DM sector
with two fields \phi_{1,2} and a $Z_3$ discrete symmetry. The DM sector only
interacts with the RHNs via a very heavy field exchange and then we can explain
the cosmic ray anomalies. With the second right-handed neutrino N_2 dominant
seesaw mechanism at the low scale around 10^4 GeV, we show that \phi_{1,2} can
obtain the vacuum expectation values around the TeV scale, and then the
lightest state from \phi_{1,2} is the decay DM with lifetime around \sim
10^{26}s. In particular, the DM very long lifetime is related to the tiny
neutrino masses, and the dominant DM decay channels to \mu and \tau are related
to the approximate \mu-\tau symmetry. Furthermore, the correct DM relic density
can be obtained via the freeze-in mechanism, the small-scale problem for power
spectrum can be solved due to the decays of the R-parity odd meta-stable states
in the DM sector, and the baryon asymmetry can be generated via the soft
leptogensis.Comment: 24 pages,3 figure

### S3 as a flavour symmetry for quarks and leptons after the Daya Bay result on \theta 13

We present a model based on the flavour group S3 X Z3 X Z6 to explain the
main features of fermion masses and mixing. In particular, in the neutrino
sector the breaking of the S3 symmetry is responsible for a naturally small
r=\Delta m^2_sol/\Delta m^2_atm and suitable next-to-leading order corrections
bring \theta 13 at the level of ~ 0.13, fully compatible with the recent Daya
Bay result. In the quark sector, the model accommodates the different mass
hierarchies in the up and down quark sectors as well as the Cabibbo angle and
Vcb (or Vub, depending on the charge assignment of the right-handed b-quark) in
the correct range.Comment: 15 pages, 3 figure

### Constrained analytical interrelations in neutrino mixing

Hermitian squared mass matrices of charged leptons and light neutrinos in the
flavor basis are studied under general additive lowest order perturbations away
from the tribimaximal (TBM) limit in which a weak basis with mass diagonal
charged leptons is chosen. Simple analytical expressions are found for the
three measurable TBM-deviants in terms of perturbation parameters appearing in
the neutrino and charged lepton eigenstates in the flavor basis. Taking
unnatural cancellations to be absent and charged lepton perturbation parameters
to be small, interrelations are derived among masses, mixing angles and the
amount of CP-violation.Comment: To be published in the Springer Proceedings in the Physics Series
under the heading of the XXI DAE-BRNS Symposium (Guwahati, India

### Fifteen Years of HFC-134a Satellite Observations: Comparisons With SLIMCAT Calculations

The phase out of anthropogenic ozone-depleting substances such as chlorofluorocarbons under the terms of the Montreal Protocol led to the development and worldwide use of hydrofluorocarbons (HFCs) in refrigeration, air conditioning, and as blowing agents and propellants. Consequently, over recent years, the atmospheric abundances of HFCs have dramatically increased. HFCs are powerful greenhouse gases and are now controlled under the terms of the 2016 Kigali Amendment to the Montreal Protocol. HFC-134a is currently the most abundant HFC in the atmosphere, breaking the 100 ppt barrier in 2018, and can be measured in the Earth's atmosphere by the satellite remote-sensing instrument ACE-FTS (Atmospheric Chemistry Experiment-Fourier Transform Spectrometer), which has been measuring since 2004. This work uses the ACE-FTS v4.0 data product to investigate global distributions and trends of HFC-134a. These measurements are compared with a simulation of SLIMCAT, a state-of-the-art three-dimensional chemical transport model, which is constrained by global surface HFC-134a measurements. The agreement between observation and model is good, although in the tropical troposphere ACE-FTS measurements are biased low by up to 10–15 ppt. The overall ACE-FTS global trend of HFC-134a for the altitude range 5.5–24.5 km and 2004–2018 time period is approximately linear with a value of 4.49 ± 0.02 ppt/year, slightly lower than the corresponding SLIMCAT trend of 4.66 ppt/year. Using a simple box model, we also estimate the annual global emissions and burdens of HFC-134a from the model data, indicating that emissions of HFC-134a have increased almost linearly, reaching 236 Gg by 2018

### Recalculation of dose for each fraction of treatment on TomoTherapy.

OBJECTIVE: The VoxTox study, linking delivered dose to toxicity requires recalculation of typically 20-37 fractions per patient, for nearly 2000 patients. This requires a non-interactive interface permitting batch calculation with multiple computers. METHODS: Data are extracted from the TomoTherapy(®) archive and processed using the computational task-management system GANGA. Doses are calculated for each fraction of radiotherapy using the daily megavoltage (MV) CT images. The calculated dose cube is saved as a digital imaging and communications in medicine RTDOSE object, which can then be read by utilities that calculate dose-volume histograms or dose surface maps. The rectum is delineated on daily MV images using an implementation of the Chan-Vese algorithm. RESULTS: On a cluster of up to 117 central processing units, dose cubes for all fractions of 151 patients took 12 days to calculate. Outlining the rectum on all slices and fractions on 151 patients took 7 h. We also present results of the Hounsfield unit (HU) calibration of TomoTherapy MV images, measured over an 8-year period, showing that the HU calibration has become less variable over time, with no large changes observed after 2011. CONCLUSION: We have developed a system for automatic dose recalculation of TomoTherapy dose distributions. This does not tie up the clinically needed planning system but can be run on a cluster of independent machines, enabling recalculation of delivered dose without user intervention. ADVANCES IN KNOWLEDGE: The use of a task management system for automation of dose calculation and outlining enables work to be scaled up to the level required for large studies.JES is supported by Cancer Research UK through the Cambridge Cancer Centre. MR, AB and KH are supported by Cancer Research UK through the VoxTox Research Programme. NGB is supported by the NIHR Cambridge Biomedical Research Centre.This is the author accepted manuscript. The final version is available from British Institute of Radiology via http://dx.doi.org/10.1259/bjr.2015077

### Ultraviolet Completion of Flavour Models

Effective Flavour Models do not address questions related to the nature of
the fundamental renormalisable theory at high energies. We study the
ultraviolet completion of Flavour Models, which in general has the advantage of
improving the predictivity of the effective models. In order to illustrate the
important features we provide minimal completions for two known A4 models. We
discuss the phenomenological implications of the explicit completions, such as
lepton flavour violating contributions that arise through the exchange of
messenger fields.Comment: 18 pages, 8 figure

### Charged Lepton Flavour Violating Radiative Decays $\ell_i \to \ell_j + \gamma$ in See-Saw Models with $A_4$ Symmetry

The charged lepton flavour violating (LFV) radiative decays, $\mu\to
e+\gamma$, $\tau\to \mu+\gamma$ and $\tau\to e +\gamma$ are investigated in a
class of supersymmetric $A_4$ models with three heavy right-handed (RH)
Majorana neutrinos, in which the lepton (neutrino) mixing is predicted to
leading order (LO) to be tri-bimaximal. The light neutrino masses are generated
via the type I see-saw mechanism. The analysis is done within the framework of
the minimal supergravity (mSUGRA) scenario, which provides flavour universal
boundary conditions at the scale of grand unification $M_X \approx 2 \times
10^{16}$ GeV. Detailed predictions for the rates of the three LFV decays are
obtained in two explicit realisations of the $A_4$ models due to Altarelli and
Feruglio and Altarelli and Meloni, respectively.Comment: Results unchanged, minor improvements made; version accepted for
publication in JHE

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