119 research outputs found

### On neutrinoless double beta decay in the minimal left-right symmetric model

We analyze the general phenomenology of neutrinoless double beta decay in the
minimal left-right symmetric model. We study under which conditions a New
Physics dominated neutrinoless double beta decay signal can be expected in the
future experiments. We show that the correlation among the different
contributions to the process, which arises from the neutrino mass generation
mechanism, can play a crucial role. We have found that, if no fine tuned
cancellation is involved in the light active neutrino contribution, a New
Physics signal can be expected mainly from the $W_R-W_R$ channel. An
interesting exception is the $W_L-W_R$ channel which can give a dominant
contribution to the process if the right-handed neutrino spectrum is
hierarchical with $M_1\lesssim$ MeV and $M_2,M_3\gtrsim$ GeV. We also discuss
if a New Physics signal in neutrinoless double beta decay experiments is
compatible with the existence of a successful Dark Matter candidate in the
left-right symmetric models. It turns out that, although it is not a generic
feature of the theory, it is still possible to accommodate such a signal with a
KeV sterile neutrino as Dark matter.Comment: 33 pages, 6 figures, references and complementary constraints added,
version accepted by European Physical Journal

### The seesaw portal in testable models of neutrino masses

A Standard Model extension with two Majorana neutrinos can explain the
measured neutrino masses and mixings, and also account for the
matter-antimatter asymmetry in a region of parameter space that could be
testable in future experiments. The testability of the model relies to some
extent on its minimality. In this paper we address the possibility that the
model might be extended by extra generic new physics which we parametrize in
terms of a low-energy effective theory. We consider the effects of the
operators of the lowest dimensionality, $d=5$, and evaluate the upper bounds on
the coefficients so that the predictions of the minimal model are robust. One
of the operators gives a new production mechanism for the heavy neutrinos at
LHC via higgs decays. The higgs can decay to a pair of such neutrinos that,
being long-lived, leave a powerful signal of two displaced vertices. We
estimate the LHC reach to this process.Comment: 19 pages, 11 figure

### The seesaw path to leptonic CP violation

Future experiments such as SHiP and high-intensity $e^+ e^-$ colliders will
have a superb sensitivity to heavy Majorana neutrinos with masses below $M_Z$.
We show that the measurement of the mixing to electrons and muons of one such
state could imply the discovery of leptonic CP violation in the context of
seesaw models. We quantify in the minimal model the CP discovery potential of
these future experiments, and demonstrate that a 5$\sigma$ CL discovery of
leptonic CP violation would be possible in a very significant fraction of
parameter space.Comment: An error has been fixed, main conclusions unchange

### Unitarity of the Leptonic Mixing Matrix

We determine the elements of the leptonic mixing matrix, without assuming
unitarity, combining data from neutrino oscillation experiments and weak
decays. To that end, we first develop a formalism for studying neutrino
oscillations in vacuum and matter when the leptonic mixing matrix is not
unitary. To be conservative, only three light neutrino species are considered,
whose propagation is generically affected by non-unitary effects. Precision
improvements within future facilities are discussed as well.Comment: Standard Model radiative corrections to the invisible Z width
included. Some numerical results modified at the percent level. Updated with
latest bounds on the rare tau decay. Physical conculsions unchange

### The discovery channel at the Neutrino Factory: $\nu_\mu\to\nu_\tau$ pointing to sterile neutrinos

We study the potential of a Neutrino Factory in constraining the parameter
space of a scheme with one sterile neutrino separated from three active ones by
an O(1) eV^2, mass-squared difference. We present approximated analytic
expressions for the oscillation probabilities, showing that the greatest
sensitivity to sterile neutrinos at a Neutrino Factory can be achieved using
the \nu_\mu ->\nu_\mu and the \nu_\mu ->\nu_\tau oscillations. We have studied
two setups: a Neutrino Factory with 50 GeV (20 GeV) stored muons, with two
detectors of the Hybrid-MIND type (a magnetized ECC next to a magnetized iron
calorimeter), located at L=3000, 7500 km (L=4000, 7500 km) from the source.
Four channels have been used: \nu_e -> \nu_\mu,\nu_\tau; \nu_\mu ->
\nu_\mu,\nu_\tau. The relevant backgrounds, efficiencies and systematic errors
have been taken into account, and we have discussed dependence of the
sensitivities on the systematic errors. We have found that the 50 GeV (20 GeV)
setup can constrain \sin^2 2 \theta^{(4fam)}_{13} <= 7x10^{-5} (2x10^{-4});
\theta_{34} <= 12 deg (14 deg); and \theta_{24}<= 7.5 deg (8 deg). Our results
hold for any value of \Delta m^2_{Sbl} >~ 0.1 eV^2. Eventually we have shown
that, if a positive signal is found, the proposed setup is able to measure
simultaneously \theta_{34} and \delta_3 with a precision of few degrees and few
tens of degrees, respectively, solving the so-called "intrinsic" and "sign
degeneracies". Combination of \nu_\mu disappearance and of the \nu_\mu
->\nu_\tau channel, that will be called "the discovery channel", at the two
baselines is able to measure at 99% CL a new CP-violating phase \delta_3 for
\sin^2 2 \theta_{34} >= 0.06.Comment: [Revised version] 58 pages, 39 figures, uses elsart.cls. Several
modifications were mad

### EURONU WP6 2009 yearly report: Update of the physics potential of Nufact, superbeams and betabeams

Many studies in the last ten years have shown that we can measure the unknown
angle theta13, discover leptonic CP violation and determine the neutrino
hierarchy in more precise neutrino oscillation experiments, searching for the
subleading channel nue -> numu in the atmospheric range. In this first report
of WP6 activities the following new results are reviewed: (1) Re-evaluation of
the physics reach of the upcoming generation of experiments to measure theta13
and delta; (2) New tools to explore a larger parameter space as needed beyond
the standard scenario; (3) Neutrino Factory: (a) evaluation of the physics
reach of a Nufact regards sterile neutrinos; (b) evaluation of the physics
reach of a Nufact as regards non-standard interactions; (c) evaluation of the
physics reach of a Nufact as regards violation of unitarity; (d) critical
assessment on long baseline tau-detection at Nufact; (e) new physics searches
at a near detector in a Nufact; (4) Beta-beams: (a) choice of ions and location
for a gamma = 100 CERN-based beta-beam; (b) re-evaluation of atmospheric
neutrino background for the gamma = 100 beta-beam scenario; (c) study of a two
baseline beta-beam; (d) measuring absolute neutrino mass with beta-beams; (e)
progress on monochromatic beta-beams; (5) Update of the physics potential of
the SPL super-beam. Eventually, we present an updated comparison of the
sensitivity to theta13, delta and the neutrino mass hierarchy of several of the
different proposed facilities.Comment: 2009 Yearly report of the Working Package 6 (Physics) of the EUROnu
FP7 EU project. 55 pages, 21 figures

### ARS leptogenesis

We review the current status of the leptogenesis scenario originally proposed by Akhmedov, Rubakov and Smirnov (ARS). It takes place in the parametric regime where the right-handed neutrinos are at the electroweak scale or below and the CP-violating effects are induced by the coherent superposition of different right-handed mass eigenstates. Two main theoretical approaches to derive quantum kinetic equations, the Hamiltonian time evolution as well as the Closed-Time-Path technique are presented, and we discuss their relations. For scenarios with two right-handed neutrinos, we chart the viable parameter space. Both, a Bayesian analysis, that determines the most likely configurations for viable leptogenesis given different variants of flat priors, and a determination of the maximally allowed mixing between the light, mostly left-handed, and heavy, mostly right-handed, neutrino states are discussed. Rephasing invariants are shown to be a useful tool to classify and to understand various distinct contributions to ARS leptogenesis that can dominate in different parametric regimes. While these analyses are carried out for the parametric regime where initial asymmetries are generated predominantly from lepton-number conserving, but flavor violating effects, we also review the contributions from lepton-number violating operators and identify the regions of parameter space where these are relevant.Fil: Drewes, Alejandro Marcelo. Technische Universitat München; AlemaniaFil: Garbrecht, B.. Technische Universitat München; AlemaniaFil: Hernández, P.. Universidad de Valencia; España. Cern - European Organization For Nuclear Research; Suiza. Université Catholique de Louvain. Particle Physics and Phenomenology. Centre for Cosmology; SuizaFil: Kekic, M.. Universidad de Valencia; EspañaFil: Lopez-Pavon, J.. Cern - European Organization For Nuclear Research; SuizaFil: Racker, Juan Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Rius, Natalia. Universidad de Valencia; EspañaFil: Salvado, J.. Universidad de Valencia; EspañaFil: Teresi, D.. Université Libre de Bruxelles; Bélgic

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