179 research outputs found
Erratum to: Maximally symmetric two Higgs doublet model with natural standard model alignment
Probes of Heavy Sterile Neutrinos
We review probes of heavy sterile neutrinos, focusing on direct experimental
searches and neutrinoless double beta decay. Working in a phenomenological
parametrization, we emphasize the importance of the nature of sterile neutrinos
in interpreting neutrinoless double beta decay searches. While current
constraints on the active-sterile neutrino mixing are already stringent, we
highlight planned future efforts that will probe regimes motivated by the
lightness of active neutrinos
Neutrinoless double beta decay via light neutralinos in R-parity violating supersymmetry
We perform a study of neutrinoless double beta (0νββ) decay mediated by the lightest neutralino of arbitrary mass in the minimal supersymmetric Standard Model (MSSM) under the presence of R-parity violating trilinear interactions. In this scenario, the exchange of the lightest neutralino can result in 0νββ decay of either long-range or short-range behaviour, depending on the neutralino mass. Using nuclear matrix elements calculated in the interacting boson model, we use an interpolation between the long- and short-range behaviours with an approximate formula. The non-observation of 0νββ decay is then used to place constraints on the supersymmetry parameter space, compatible with constraints from collider experiments. We compare these constraints to bounds from pion decays, CKM unitarity and big bang nucleosynthesis
Stable fermion mass matrices and the charged lepton contribution to neutrino mixing
We study the general properties of hierarchical fermion mass matrices in which the small eigenvalues are stable with respect to perturbations of the matrix entries and we consider specific applications to the charged lepton contribution to neutrino mixing. In particular, we show that the latter can account for the whole lepton mixing. In this case a value of sin \u3b813 73 me/m\u3bcsin \u3b823 48 0.03, as observed, can be obtained without the need of any fine-tuning, and present data allow to determine the last row of the charged lepton mass matrix with good accuracy. We also consider the case in which the neutrino sector only provides a maximal 12 rotation and show that i) present data provide a 2\u3c3 evidence for a non-vanishing 31 entry of the charged lepton mass matrix and ii) a plausible texture for the latter can account at the same time for the atmospheric mixing angle, the \u3b813angle, and the deviation of the \u3b812angle from \u3c0/2 without fine-tuning or tension with data. Finally, we show that the so-called \u201cinverted order\u201d of the 12 and 23 rotations in the charged lepton sector can be obtained without fine-tuning, up to corrections of order me/m\u3bc. \ua9 2014, The Author(s)
Does the `Higgs' have Spin Zero?
The Higgs boson is predicted to have spin zero. The ATLAS and CMS experiments
have recently reported of an excess of events with mass ~ 125 GeV that has some
of the characteristics expected for a Higgs boson. We address the questions
whether there is already any evidence that this excess has spin zero, and how
this possibility could be confirmed in the near future. The excess observed in
the gamma gamma final state could not have spin one, leaving zero and two as
open possibilities. We calculate the angular distribution of gamma gamma pairs
from the decays of a spin-two boson produced in gluon-gluon collisions, showing
that is unique and distinct from the spin-zero case. We also calculate the
distributions for lepton pairs that would be produced in the W W* decays of a
spin-two boson, which are very different from those in Higgs decays, and note
that the kinematics of the event selection used to produce the excess observed
in the W W* final state have reduced efficiency for spin two.Comment: 22 pages, 22 figures, Version accepted for publication in JHEP,
includes additional plots of dilepton mass distribution
A model of neutrino mass and dark matter with large neutrinoless double beta decay
We propose a model where neutrino masses are generated at three loop order but neutrinoless double beta decay occurs at one loop. Thus we can have large neutrinoless double beta decay observable in the future experiments even when the neutrino masses are very small. The model receives strong constraints from the neutrino data and lepton flavor violating decays, which substantially reduces the number of free parameters. Our model also opens up the possibility of having several new scalars below the TeV regime, which can be explored at the collider experiments. Additionally, our model also has an unbroken Z2 symmetry which allows us to identify a viable Dark Matter candidate
Sneutrino dark matter in low-scale seesaw scenarios
We consider supersymmetric models in which sneutrinos are viable dark matter candidates. These are either simple extensions of the Minimal Supersymmetric Standard Model with additional singlet superfields, such as the inverse or linear seesaw, or a model with an additional U(1) group. All of these models can accomodate the observed small neutrino masses and large mixings. We investigate the properties of sneutrinos as dark matter candidates in these scenarios. We check for phenomenological bounds, such as correct relic abundance, consistency with direct detection cross section limits and laboratory constraints, among others lepton flavour violating (LFV) charged lepton decays. While inverse and linear seesaw lead to different results for LFV, both models have very similar dark matter phenomenology, consistent with all experimental bounds. The extended gauge model shows some additional and peculiar features due to the presence of an extra gauge boson Z' and an additional light Higgs. Specifically, we point out that for sneutrino LSPs there is a strong constraint on the mass of the Z' due to the experimental bounds on the direct detection scattering cross section
A realistic pattern of fermion masses from a five-dimensional SO(10) model
We provide a unified description of fermion masses and mixing angles in the
framework of a supersymmetric grand unified SO(10) model with anarchic Yukawa
couplings of order unity. The space-time is five dimensional and the extra flat
spatial dimension is compactified on the orbifold ,
leading to Pati-Salam gauge symmetry on the boundary where Yukawa interactions
are localised. The gauge symmetry breaking is completed by means of a rather
economic scalar sector, avoiding the doublet-triplet splitting problem. The
matter fields live in the bulk and their massless modes get exponential
profiles, which naturally explain the mass hierarchy of the different fermion
generations. Quarks and leptons properties are naturally reproduced by a
mechanism, first proposed by Kitano and Li, that lifts the SO(10) degeneracy of
bulk masses in terms of a single parameter. The model provides a realistic
pattern of fermion masses and mixing angles for large values of . It
favours normally ordered neutrino mass spectrum with the lightest neutrino mass
below 0.01 eV and no preference for leptonic CP violating phases. The right
handed neutrino mass spectrum is very hierarchical and does not allow for
thermal leptogenesis. We analyse several variants of the basic framework and
find that the results concerning the fermion spectrum are remarkably stable.Comment: 30 pages, 7 figures, 4 table
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