3,877 research outputs found

    The Dark Side of θ13\theta_{13}, δCP\delta_{CP}, Leptogenesis and Inflation in Type-I Seesaw

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    In the context of the type-I seesaw mechanism, it is known that θ13\theta_{13} is zero and leptogenesis can not be realized if there exists a residual flavor symmetry resulting in the Tri-Bimaximal neutrino mixing pattern. We propose a simple framework where additional particles, odd under a Z2Z_2 symmetry, break the residual flavor symmetry and the lightest of the Z2Z_2 odd particles is the dark matter candidate. As as result, nonzero θ13\theta_{13}, δCP\delta_{CP}, leptogenesis and the correct dark matter density can be accommodated. On the other hand, a Z2Z_2 odd scalar can play the role of the inflaton with mass of 101310^{13} GeV motivated by the recent BICEP2 results. Interestingly, the model can "generate" δCP≃−π/2\delta_{CP} \simeq -\pi/2, preferred by the T2K experiment in the normal hierarchy neutrino mass spectrum.Comment: 23 pages, 8 Figures and 5 Tables. v3: a toy A4 flavor model provided, version accepted by JHE

    Dark Matter and Lepton Flavour Violation in a Hybrid Neutrino Mass Model

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    We describe a hybrid model in which the light neutrino mass matrix receives both tree-level seesaw and loop-induced contributions. An additional U(1) gauge symmetry is used to stabilize the lightest right-handed neutrino as the Dark Matter candidate. After fitting the experimental neutrino data, we analyze and correlate the phenomenological consequences of the model, namely its impact on electroweak precision measurements, the Dark Matter relic abundance, lepton flavour violating rare decays and neutrinoless double beta decay. We find that natural realizations of the model characterized by large Yukawa couplings are compatible with and close to the current experimental limits.Comment: 25 pages, 9 figures. V2: references added, typos corrected, version accepted by JHE

    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−WRW_R-W_R channel. An interesting exception is the WL−WRW_L-W_R channel which can give a dominant contribution to the process if the right-handed neutrino spectrum is hierarchical with M1≲M_1\lesssim MeV and M2,M3≳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

    Constraining the (Low-Energy) Type-I Seesaw

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    The type-I seesaw Lagrangian yields a non-generic set of active-sterile oscillation parameters - the neutrino mass eigenvalues and the physical elements of the full mixing matrix are entwined. For this reason one is able to, in principle, test the model by performing enough measurements which are sensitive to neutrino masses and lepton mixing. We point out that for light enough right-handed neutrino masses - less than 10 eV - next-generation short-baseline neutrino oscillation experiments may be able to unambiguously rule out (or "rule in") the low energy seesaw as the Lagrangian that describes neutrino masses. These types of searches are already under consideration in order to address the many anomalies from accelerator neutrino experiments (LSND, MiniBooNe), reactor neutrino experiments (the "reactor anomaly") and others. In order to test the low-energy seesaw, it is crucial to explore different oscillation channels, including nu_e and nu_mu disappearance and nu_mu to nu_tau appearance.Comment: 15 pages, five figure

    Polarized gamma rays from dark matter annihilations

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    In this paper, we explore the possibility of a linearly polarized gamma-ray signal from dark matter annihilations in the Galactic center. Considering neutral weakly interacting massive particles, a polarized gamma-ray signal can be realized by a two-component dark matter model of Majorana fermions with an anapole moment. We discuss the spin alignment of such dark matter fermions in the Galactic center and then estimate the intensity and the polarizability of the final-state electromagnetic radiation in the dark matter annihilations. For low-mass dark matter, the photon flux at sub-GeV energies may be polarized at a level detectable in current X-ray polarimeters. Depending on the mass ratio between the final-state fermion and DM, the degree of polarization at the mass threshold can reach 70%70\% or even higher, providing us with a new tool for probing the nature of dark matter in future gamma-ray polarization experiments.Comment: 19 pages, 7 figures. v2: version accepted by Physics Letters
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