119 research outputs found

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

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    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 WR‚ąíWRW_R-W_R channel. An interesting exception is the WL‚ąíWRW_L-W_R channel which can give a dominant contribution to the process if the right-handed neutrino spectrum is hierarchical with M1‚Č≤M_1\lesssim MeV and M2,M3‚Č≥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

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    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=5d=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

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    Future experiments such as SHiP and high-intensity e+e‚ąíe^+ e^- colliders will have a superb sensitivity to heavy Majorana neutrinos with masses below MZM_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 5ŌÉ\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

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    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: őĹőľ‚ÜíőĹŌĄ\nu_\mu\to\nu_\tau pointing to sterile neutrinos

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    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

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    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

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    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 M√ľnchen; AlemaniaFil: Garbrecht, B.. Technische Universitat M√ľnchen; AlemaniaFil: Hern√°ndez, P.. Universidad de Valencia; Espa√Īa. Cern - European Organization For Nuclear Research; Suiza. Universit√© Catholique de Louvain. Particle Physics and Phenomenology. Centre for Cosmology; SuizaFil: Kekic, M.. Universidad de Valencia; Espa√ĪaFil: Lopez-Pavon, J.. Cern - European Organization For Nuclear Research; SuizaFil: Racker, Juan Diego. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Centro Cient√≠fico Tecnol√≥gico Conicet - C√≥rdoba. Instituto de Astronom√≠a Te√≥rica y Experimental. Universidad Nacional de C√≥rdoba. Observatorio Astron√≥mico de C√≥rdoba. Instituto de Astronom√≠a Te√≥rica y Experimental; ArgentinaFil: Rius, Natalia. Universidad de Valencia; Espa√ĪaFil: Salvado, J.. Universidad de Valencia; Espa√ĪaFil: Teresi, D.. Universit√© Libre de Bruxelles; B√©lgic
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