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Hirsch, M., Srivastava, R., & Valle, J. W. F. (2018). Can one ever prove that neutrinos are Dirac particles? Phys. Lett. B, 781, 302–305.
Abstract: According to the “Black Box” theorem the experimental confirmation of neutrinoless double beta decay (0 nu 2 beta) would imply that at least one of the neutrinos is a Majorana particle. However, a null 0 nu 2 beta signal cannot decide the nature of neutrinos, as it can be suppressed even for Majorana neutrinos. In this letter we argue that if the null 0 nu 2 beta decay signal is accompanied by a 0 nu 2 beta quadruple beta decay signal, then at least one neutrino should be a Dirac particle. This argument holds irrespective of the underlying processes leading to such decays.
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Centelles Chulia, S., Srivastava, R., & Valle, J. W. F. (2018). Seesaw Dirac neutrino mass through dimension-six operators. Phys. Rev. D, 98(3), 035009–18pp.
Abstract: In this paper, a follow-up of [S. C. Chulia, R. Srivastava, and J. W. F. Valle, Phys. Lett. B 781, 122 (2018)], we describe the many pathways to generate Dirac neutrino mass through dimension-six operators. By using only the standard model Higgs doublet in the external legs, one gets a unique operator 1/Lambda(2) (L) over bar (Phi) over bar (Phi) over bar Phi nu(R). In contrast, the presence of new scalars implies new possible field contractions, which greatly increase the number of possibilities. Here, we study in detail the simplest ones, involving SU(2)(L) singlets, doublets, and triplets. The extra symmetries needed to ensure the Dirac nature of neutrinos can also be responsible for stabilizing dark matter.
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de Campos, F., Eboli, O. J. P., Hirsch, M., Magro, M. B., Porod, W., Restrepo, D., et al. (2010). Probing neutrino oscillations in supersymmetric models at the Large Hadron Collider. Phys. Rev. D, 82(7), 075002–8pp.
Abstract: The lightest supersymmetric particle may decay with branching ratios that correlate with neutrino oscillation parameters. In this case the CERN Large Hadron Collider (LHC) has the potential to probe the atmospheric neutrino mixing angle with sensitivity competitive to its low-energy determination by underground experiments. Under realistic detection assumptions, we identify the necessary conditions for the experiments at CERN's LHC to probe the simplest scenario for neutrino masses induced by minimal supergravity with bilinear R parity violation.
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Esteves, J. N., Joaquim, F. R., Joshipura, A. S., Romao, J. C., Tortola, M., & Valle, J. W. F. (2010). A(4)-based neutrino masses with Majoron decaying dark matter. Phys. Rev. D, 82(7), 073008–8pp.
Abstract: We propose an A(4) flavor-symmetric SU(3) circle times SU(2) circle times U(1) seesaw model where lepton number is broken spontaneously. A consistent two-zero texture pattern of neutrino masses and mixing emerges from the interplay of type-I and type-II seesaw contributions, with important phenomenological predictions. We show that, if the Majoron becomes massive, such seesaw scenario provides a viable candidate for decaying dark matter, consistent with cosmic microwave background lifetime constraints that follow from current WMAP observations. We also calculate the subleading one-loop-induced decay into photons which leads to a monoenergetic emission line that may be observed in future x-ray missions such as Xenia.
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Escrihuela, F. J., Tortola, M., Valle, J. W. F., & Miranda, O. G. (2011). Global constraints on muon-neutrino nonstandard interactions. Phys. Rev. D, 83(9), 093002–8pp.
Abstract: The search for new interactions of neutrinos beyond those of the standard model may help to elucidate the mechanism responsible for neutrino masses. Here, we combine existing accelerator neutrino data with restrictions coming from a recent atmospheric neutrino data analysis in order to lift parameter degeneracies and improve limits on new interactions of muon neutrinos with quarks. In particular, we reconsider the results of the E-815 experiment at Fermilab (NuTeV) in view of a new evaluation of its systematic uncertainties. We find that, although constraints for muon neutrinos are better than those applicable to tau or electron neutrinos, they lie at the few X 10(-2) level, not as strong as previously believed. We briefly discuss prospects for further improvement.
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Bazzocchi, F., Cerdeño, D. G., Muñoz, C., & Valle, J. W. F. (2010). Calculable inverse-seesaw neutrino masses in supersymmetry. Phys. Rev. D, 81(5), 051701–5pp.
Abstract: We provide a scenario where naturally small and calculable neutrino masses arise from a supersymmetry-breaking renormalization-group-induced vacuum expectation value. The construction consists of an extended version of the next-to-minimal supersymmetric standard model and the mechanism is illustrated for a universal choice of the soft supersymmetry-breaking parameters. The lightest supersymmetric particle can be an isosinglet scalar neutrino state, potentially viable as WIMP dark matter through its Higgs new boson coupling. The scenario leads to a plethora of new phenomenological implications at accelerators including the Large Hadron Collider.
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Esteban-Pretel, A., Tomas, R., & Valle, J. W. F. (2010). Interplay between collective effects and nonstandard interactions of supernova neutrinos. Phys. Rev. D, 81(6), 063003–16pp.
Abstract: We consider the effect of nonstandard neutrino interactions (NSI, for short) on the propagation of neutrinos through the supernova (SN) envelope within a three-neutrino framework and taking into account the presence of a neutrino background. We find that for given NSI parameters, with strength generically denoted by epsilon(ij), neutrino evolution exhibits a significant time dependence. For vertical bar epsilon(tau tau)vertical bar greater than or similar to 10(-3) the neutrino survival probability may become sensitive to the V-23 octant and the sign of epsilon(tau tau). In particular, if epsilon(tau tau) greater than or similar to 10(-2) an internal I-resonance may arise independently of the matter density. For typical values found in SN simulations this takes place in the same dense-neutrino region above the neutrinosphere where collective effects occur, in particular, during the synchronization regime. This resonance may lead to an exchange of the neutrino fluxes entering the bipolar regime. The main consequences are (i) bipolar conversion taking place for normal neutrino mass hierarchy and (ii) a transformation of the flux of low-energy v(e), instead of the usual spectral swap.
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Schwetz, T., Tortola, M., & Valle, J. W. F. (2011). Global neutrino data and recent reactor fluxes: the status of three-flavour oscillation parameters. New J. Phys., 13, 063004–15pp.
Abstract: We present the results of a global neutrino oscillation data analysis within the three-flavour framework. We include the latest results from the MINOS long-baseline experiment (including electron neutrino appearance and anti-neutrino data), updating all relevant solar (Super-Kamiokande (SK) II + III), atmospheric (SK I + II + III) and reactor (KamLAND) data. Furthermore, we include a recent re-calculation of the anti-neutrino fluxes emitted from nuclear reactors. These results have important consequences for the analysis of reactor experiments and in particular for the status of the mixing angle theta(13). In our recommended default analysis, we find from the global fit that the hint for nonzero theta(13) remains weak, at 1.8 sigma for both neutrino mass hierarchy schemes. However, we discuss in detail the dependence of these results on assumptions regarding the reactor neutrino analysis.
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Morisi, S., Peinado, E., Shimizu, Y., & Valle, J. W. F. (2011). Relating quarks and leptons without grand unification. Physical Review D, 84(3), 036003.
Abstract: In combination with supersymmetry, flavor symmetry may relate quarks with leptons, even in the absence of a grand-unification group. We propose an SU(3) x SU(2) x U(1) model where both supersymmetry and the assumed A(4) flavor symmetries are softly broken, reproducing well the observed fermion mass hierarchies and predicting: (i) a relation between down-type quarks and charged lepton masses, and (ii) a correlation between the Cabibbo angle in the quark sector and the reactor angle theta(13) characterizing CP violation in neutrino oscillations.
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Rodejohann, W., & Valle, J. W. F. (2011). Symmetrical parametrizations of the lepton mixing matrix. Phys. Rev. D, 84(7), 073011–6pp.
Abstract: Advantages of the original symmetrical form of the parametrization of the lepton mixing matrix are discussed. It provides a conceptually more transparent description of neutrino oscillations and lepton number violating processes like neutrinoless double beta decay, clarifying the significance of Dirac and Majorana phases. It is also ideal for parametrizing scenarios with light sterile neutrinos.
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