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Kosmas, T. S., Miranda, O. G., Papoulias, D. K., Tortola, M., & Valle, J. W. F. (2015). Sensitivities to neutrino electromagnetic properties at the TEXONO experiment. Phys. Lett. B, 750, 459–465.
Abstract: The possibility of measuring neutral-current coherent elastic neutrino nucleus scattering (CENNS) at the TEXONO experiment has opened high expectations towards probing exotic neutrino properties. Focusing on low threshold Germanium-based targets with kg-scale mass, we find a remarkable efficiency not only for detecting CENNS events due to the weak interaction, but also for probing novel electromagnetic neutrino interactions. Specifically, we demonstrate that such experiments are complementary in performing precision Standard Model tests as well as in shedding light on sub-leading effects due to neutrino magnetic moment and neutrino charge radius. This work employs realistic nuclear structure calculations based on the quasi-particle random phase approximation (QRPA) and takes into consideration the crucial quenching effect corrections. Such a treatment, in conjunction with a simple statistical analysis, shows that the attainable sensitivities are improved by one order of magnitude as compared to previous studies.
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Chen, P., Ding, G. J., Rojas, A. D., Vaquera-Araujo, C. A., & Valle, J. W. F. (2016). Warped flavor symmetry predictions for neutrino physics. J. High Energy Phys., 01(1), 007–27pp.
Abstract: A realistic five-dimensional warped scenario with all standard model fields propagating in the bulk is proposed. Mass hierarchies would in principle be accounted for by judicious choices of the bulk mass parameters, while fermion mixing angles are restricted by a Delta(27) flavor symmetry broken on the branes by flavon fields.The latter gives stringent predictions for the neutrino mixing parameters, and the Dirac CP violation phase, all described in terms of only two independent parameters at leading order. The scheme also gives an adequate CKM fit and should be testable within upcoming oscillation experiments.
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Cañas, B. C., Miranda, O. G., Parada, A., Tortola, M., & Valle, J. W. F. (2016). Updating neutrino magnetic moment constraints. Phys. Lett. B, 753, 191–198.
Abstract: In this paper we provide an updated analysis of the neutrino magnetic moments (NMMs), discussing both the constraints on the magnitudes of the three transition moments Lambda(i) and the role of the CP violating phases present both in the mixing matrix and in the NMM matrix. The scattering of solar neutrinos off electrons in Borexino provides the most stringent restrictions, due to its robust statistics and the low energies observed, below 1 MeV. Our new limit on the effective neutrino magnetic moment which follows from the most recent Borexino data is 3.1 x 10(-11) mu(B) at 90% C.L. This corresponds to the individual transition magnetic moment constraints: vertical bar Lambda(1)vertical bar <= 5.6 x10(-11)mu(B), vertical bar Lambda(2)vertical bar <= 4.0 x10(-11)mu(B), and vertical bar Lambda(3)vertical bar <= 3.1 x10(-11)mu B(90% C. L.), irrespective of any complex phase. Indeed, the incoherent admixture of neutrino mass eigenstates present in the solar flux makes Borexino insensitive to the Majorana phases present in the NMM matrix. For this reason we also provide a global analysis including the case of reactor and accelerator neutrino sources, presenting the resulting constraints for different values of the relevant CP phases. Improved reactor and accelerator neutrino experiments will be needed in order to underpin the full profile of the neutrino electromagnetic properties.
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Chen, P., Ding, G. J., Gonzalez-Canales, F., & Valle, J. W. F. (2016). Generalized mu-tau reflection symmetry and leptonic CP violation. Phys. Lett. B, 753, 644–652.
Abstract: We propose a generalized mu-tau reflection symmetry to constrain the lepton flavor mixing parameters. We obtain a new correlation between the atmospheric mixing angle theta(23) and the “Dirac” CP violation phase delta(CP). Only in a specific limit our proposed CP transformation reduces to standard mu-tau reflection, for which theta(23) and delta(CP) are both maximal. The “Majorana” phases are predicted to lie at their CP-conserving values with important implications for the neutrinoless double beta decay rates. We also study the phenomenological implications of our scheme for present and future neutrino oscillation experiments including T2K, NO nu A and DUNE.
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Bonilla, C., Romao, J. C., & Valle, J. W. F. (2016). Electroweak breaking and neutrino mass: `invisible' Higgs decays at the LHC (type II seesaw). New J. Phys., 18, 033033–21pp.
Abstract: Neutrino mass generation through the Higgs mechanism not only suggests the need to reconsider the physics of electroweak symmetry breaking from a new perspective, but also provides a new theoretically consistent and experimentally viable paradigm. We illustrate this by describing the main features of the electroweak symmetry breaking sector of the simplest type-II seesaw model with spontaneous breaking of lepton number. After reviewing the relevant `theoretical' and astrophysical restrictions on the Higgs sector, we perform an analysis of the sensitivities of Higgs Boson searches at the ongoing ATLAS and CMS experiments at the LHC, including not only the new contributions to the decay channels present in the standard model (SM) but also genuinely non-SM Higgs Boson decays, such as `invisible' Higgs Boson decays to majorons. We find sensitivities that are likely to be reached at the upcoming run of the experiments.
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Bonilla, C., Fonseca, R. M., & Valle, J. W. F. (2016). Vacuum stability with spontaneous violation of lepton number. Phys. Lett. B, 756, 345–349.
Abstract: The vacuum of the Standard Model is known to be unstable for the measured values of the top and Higgs masses. Here we show how vacuum stability can be achieved naturally if lepton number is violated spontaneously at the TeV scale. More precise Higgs measurements in the next LHC run should provide a crucial test of our symmetry breaking scenario. In addition, these schemes typically lead to enhanced rates for processes involving lepton flavor violation.
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Bonilla, C., Nebot, M., Valle, J. W. F., & Srivastava, R. (2016). Flavor physics scenario for the 750 GeV diphoton anomaly. Phys. Rev. D, 93(7), 073009–5pp.
Abstract: A simple variant of a realistic flavor symmetry scheme for fermion masses and mixings provides a possible interpretation of the diphoton anomaly as an electroweak singlet “flavon.” The existence of TeV scale vectorlike T-quarks required to provide adequate values for Cabibbo-Kobayashi-Maskawa (CKM) parameters can also naturally account for the diphoton anomaly. Correlations between V-ub and V-cb with the vectorlike T-quark mass can be predicted. Should the diphoton anomaly survive in a future run, our proposed interpretation can also be tested in upcoming B and LHC studies.
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Valle, J. W. F., & Vaquera-Araujo, C. A. (2016). Dynamical seesaw mechanism for Dirac neutrinos. Phys. Lett. B, 755, 363–366.
Abstract: So far we have not been able to establish that, as theoretically expected, neutrinos are their own anti-particles. Here we propose a dynamical way to account for the Dirac nature of neutrinos and the smallness of their mass in terms of a new variant of the seesaw paradigm in which the energy scale of neutrino mass generation could be accessible to the current LHC experiments.
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Miranda, O. G., & Valle, J. W. F. (2016). Neutrino oscillations and the seesaw origin of neutrino mass. Nucl. Phys. B, 908, 436–455.
Abstract: The historical discovery of neutrino oscillations using solar and atmospheric neutrinos, and subsequent accelerator and reactor studies, has brought neutrino physics to the precision era. We note that CP effects in oscillation phenomena could be difficult to extract in the presence of unitarity violation. As a result upcoming dedicated leptonic CP violation studies should take into account the non-unitarity of the lepton mixing matrix. Restricting non-unitarity will shed light on the seesaw scale, and thereby guide us towards the new physics responsible for neutrino mass generation.
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Merle, A., Platscher, M., Rojas, N., Valle, J. W. F., & Vicente, A. (2016). Consistency of WIMP Dark Matter as radiative neutrino mass messenger. J. High Energy Phys., 07(7), 013–17pp.
Abstract: The scotogenic scenario provides an attractive approach to both Dark Matter and neutrino mass generation, in which the same symmetry that stabilises Dark Matter also ensures the radiative seesaw origin of neutrino mass. However the simplest scenario may suffer from inconsistencies arising from the spontaneous breaking of the underlying Z(2) symmetry. Here we show that the singlet-triplet extension of the simplest model naturally avoids this problem due to the presence of scalar triplets neutral under the Z(2) which affect the evolution of the couplings in the scalar sector. The scenario offers good prospects for direct WIMP Dark Matter detection through the nuclear recoil method.
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