187 research outputs found
Probing the Majorana nature of the neutrino with neutrinoless double beta decay
Neutrinoless double beta decay (NDBD) is the only experiment that could probe
the Majorana nature of the neutrino. Here we study the theoretical implications
of NDBD for models yielding tri-bimaximal lepton mixing like A4 and S4.Comment: Talk given at TAUP09, July 1-5, 2009 (Roma).The proceeding will be
published in Journal of Physics, Conference Series (Editors: E. Coccia, L.
Pandola, N. Fornengo, R. Aloisio
Cosmogenic neutrino fluxes under the effect of active-sterile secret interactions
Ultra High Energy cosmogenic neutrinos may represent a unique opportunity to
unveil possible new physics interactions once restricted to the neutrino sector
only. In the present paper we study the observable effects of a secret
active-sterile interactions, mediated by a pseudoscalar, on the expected flux
of cosmogenic neutrinos. The results show that for masses of sterile neutrinos
and pseudoscalars of hundreds MeV, necessary to evade cosmological,
astrophysical and elementary particle constraints, the presence of such new
interactions can significantly change the energy spectrum of cosmogenic
neutrinos at Earth in the energy range from PeV to ZeV. Interestingly, the
distortion of the spectrum results to be detectable at GRAND apparatus if the
scalar mediator mass is around 250 MeV and the UHECRs are dominated by the
proton component. Larger mediator masses or a chemical composition of UHECRs
dominated by heavier nuclei would require much larger cosmic rays apparatus
which might be available in future.Comment: 10 pages, 3 figure
Inverse tri-bimaximal type-III seesaw and lepton flavor violation
We present a type-III version of inverse seesaw or, equivalently an inverse
version of type-III seesaw. Naturally small neutrino masses arise at low-scale
from the exchange of neutral fermions transforming as hyperchargeless SU(2)
triplets. In order to implement tri-bimaximal lepton mixing we supplement the
minimal SU(3)xSU(2)xU(1) gauge symmetry with an A4-based flavor symmetry. Our
scenario induces lepton flavour violating (LFV) three body decays that can
proceed at the tree level, while radiative li to lj gamma decays and mu-e
conversion in nuclei are also expected to be sizeable. LFV decays are related
by the underlying flavor symmetry and the new fermions are also expected to be
accessible for study at the Large Hadron Collider (LHC)
A new neutrino mass sum rule from inverse seesaw
A class of discrete flavor-symmetry-based models predicts constrained
neutrino mass matrix schemes that lead to specific neutrino mass sum-rules
(MSR). One of these implies in a lower bound on the effective neutrinoless
double beta mass parameter, even for normal hierarchy neutrinos. Here we
propose a new model based on the S4 flavor symmetry that leads to the new
neutrino mass sum-rule and discuss how to generate a nonzero value for the
reactor mixing angle indicated by recent experiments, and the resulting
correlation with the solar mixing angle.Comment: 14 pages, 4 figure
A SUSY A4 model for fermion masses and mixings
We study a supersymmetric extension of the Standard Model based on discrete
A4xZ3xZ4 flavor symmetry. We obtain quark mixing angles as well as a realistic
fermion mass spectrum and we predict tribimaximal leptonic mixing by a
spontaneous breaking of A4. The top quark Yukawa interaction is present at the
renormalizable level in the superpotential while all the other Yukawa
interactions arise only at higher orders. We study the Higgs potential and show
that it can potentially solve the so called vacuum alignment problem. The
leading order predictions are not spoiled by subleading corrections.Comment: version accepted in JHEP, Z3xZ2 changed in Z3xZ4, typos in table
corrected, references adde
Gauge boson families in grand unified theories of fermion masses: E_6^4 x S_4
In third quantization the origin of fermion families is easy to understand:
the electron field, the muon field and the tau field are identical fields in
precisely the same sense as three electrons are identical and undistinguishable
particles of a theory of second quantization. In both cases, the permutation of
these fields or particles leaves the lagrangian invariant. One can also extend
the concept of family to gauge bosons. This can be obtained through the
semidirect product of the gauge group with the group of permutations of n
objects. In this paper we have studied the group E_6^4 x S_4. We explain why we
have chosen E_6 as fundamental gauge group factor and why we start with a model
with four gauge boson/fermion families to accommodate and to fit the standard
model with only three fermion families. We suggest a possible symmetry breaking
pattern of E_6^4 x S_4 that could explain quark, lepton and neutrino masses and
mixings.Comment: 21 pages, no figur
A Simplest A4 Model for Tri-Bimaximal Neutrino Mixing
We present a see-saw model for Tri-Bimaximal mixing which is based on a
very economical flavour symmetry and field content and still possesses all the
good features of models. In particular the charged lepton mass
hierarchies are determined by the flavour symmetry itself
without invoking a Froggatt-Nielsen U(1) symmetry. Tri-Bimaximal mixing is
exact in leading order while all the mixing angles receive corrections of the
same order in next-to-the-leading approximation. As a consequence the predicted
value of is within the sensitivity of the experiments which will
take data in the near future. The light neutrino spectrum, typical of
see-saw models, with its phenomenological implications, also including
leptoproduction, is studied in detail.Comment: 20 pages, 2 figure
Which criteria should we use to end isolation in hemodialysis patients with COVID-19?
Safe and timely discontinuation of quarantine of in-center hemodialysis (HD) patients with a previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is a challenging issue for the nephrological community because current guidelines for ending isolation do not mention dialysis patients. To prevent potentially fatal outbreaks of coronavirus disease 2019 (COVID-19), a cautionary approach has been adopted by most dialysis units. The criteria for ending the isolation in the HD population generally coincide with those recommended for immunocompromised people. Thus, a test-based strategy relying on two consecutive negative reverse transcriptase-polymerase chain reaction (RT-PCR) nasopharyngeal swabs has been adopted to terminate quarantine. This strategy has the disadvantage of prolonging isolation as RT-PCR positivity does not equate to SARS-CoV-2 infectivity. Consequentially, prolonged positivity of SARS-CoV-2 results in excessive workload for the HD staff who must face an increasing number of COVID-19 patients requiring isolation. This condition leads also to serious implications for the patients and their households including work productivity loss, postponement of health-care appointments and an increased risk of COVID-19 reinfection. To counteract this problem, other diagnostic tests should be used to provide the best care to HD patients. Recent results seem to encourage the use of RT-PCR cycle threshold (Ct) values and rapid antigen tests given their better correlation with cell culture for SARS-CoV-2 than RT-PCR testing. Here, we provide an overview of the current scientific evidence on the tests used to verify the infectiousness of the virus in order to stimulate the nephrological community to adopt a streamlined and pragmatic procedure to end isolation in COVID-19 patients on HD
Neutrino phenomenology from leptogenesis
Assuming a type-I seesaw mechanism for neutrino mass generation and invoking
a baryogengesis via leptogenesis scenario, we consider a reasonable
hierarchical structure for Dirac neutrino mass matrix, similar to up-type quark
mass matrix. These hypotheses imply a relevant connection between high scale CP
violation and low energy one. By requiring a compact heavy neutrino mass
spectrum, which allows to circumvent Davidson-Ibarra limit, one can obtain an
efficient leptogenesis restricting the allowed region for low energy neutrino
parameters. Once the oscillating parameters are taken inside a range,
through the numerical resolution of the leptogenesis Boltzmann equations one
gets the following allowed intervals for the lightest neutrino mass and the
Dirac CP phase: and eV.Comment: 15 pages, 2 figure
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