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Pierre Auger Collaboration(Abreu, P. et al), & Pastor, S. (2012). Search for Point-like Sources of Ultra-high Energy Neutrinos at the Pierre Auger Observatory and Improved Limit on the Diffuse Flux of Tau Neutrinos. Astrophys. J. Lett., 755(1), L4–7pp.
Abstract: The surface detector array of the Pierre Auger Observatory can detect neutrinos with energy E-nu between 10(17) eV and 10(20) eV from point-like sources across the sky south of +55 degrees and north of -65 degrees declinations. A search has been performed for highly inclined extensive air showers produced by the interaction of neutrinos of all flavors in the atmosphere (downward-going neutrinos), and by the decay of tau leptons originating from tau neutrino interactions in Earth's crust (Earth-skimming neutrinos). No candidate neutrinos have been found in data up to 2010 May 31. This corresponds to an equivalent exposure of similar to 3.5 years of a full surface detector array for the Earth-skimming channel and similar to 2 years for the downward-going channel. An improved upper limit on the diffuse flux of tau neutrinos has been derived. Upper limits on the neutrino flux from point-like sources have been derived as a function of the source declination. Assuming a differential neutrino flux k(PS) . E-nu(-2). from a point-like source, 90% confidence level upper limits for k(PS) at the level of approximate to 5x10(-7) and 2.5x10(-6) GeV cm(-2) s(-1) have been obtained over a broad range of declinations from the searches for Earth-skimming and downward-going neutrinos, respectively.
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Coloma, P., Donini, A., Fernandez-Martinez, E., & Hernandez, P. (2012). Precision on leptonic mixing parameters at future neutrino oscillation experiments. J. High Energy Phys., 06(6), 073–27pp.
Abstract: We perform a comparison of the different future neutrino oscillation experiments based on the achievable precision in the determination of the fundamental parameters theta(13) and the CP phase, delta, assuming that theta(13) is in the range indicated by the recent Daya Bay measurement. We study the non-trivial dependence of the error on delta on its true value. When matter effects are small, the largest error is found at the points where CP violation is maximal, and the smallest at the CP conserving points. The situation is different when matter effects are sizable. As a result of this effect, the comparison of the physics reach of different experiments on the basis of the CP discovery potential, as usually done, can be misleading. We have compared various proposed super-beam, beta-beam and neutrino factory setups on the basis of the relative precision of theta(13) and the error on delta. Neutrino factories, both high-energy or low-energy, outperform alternative beam technologies. An ultimate precision on theta(13) below 3% and an error on delta of <= 7 degrees at 1 sigma (1 d.o.f.) can be obtained at a neutrino factory.
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Aparici, A., Herrero-Garcia, J., Rius, N., & Santamaria, A. (2012). On the nature of the fourth generation neutrino and its implications. J. High Energy Phys., 07(7), 030–31pp.
Abstract: We consider the neutrino sector of a Standard Model with four generations. While the three light neutrinos can obtain their masses from a variety of mechanisms with or without new neutral fermions, fourth-generation neutrinos need at least one new relatively light right-handed neutrino. If lepton number is not conserved this neutrino must have a Majorana mass term whose size depends on the underlying mechanism for lepton number violation. Majorana masses for the fourth-generation neutrinos induce relative large two-loop contributions to the light neutrino masses which could be even larger than the cosmological bounds. This sets strong limits on the mass parameters and mixings of the fourth-generation neutrinos.
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Barenboim, G., & Rasero, J. (2012). Electroweak baryogenesis window in non standard cosmologies. J. High Energy Phys., 07(7), 028–20pp.
Abstract: In this work we show that the new bounds on the Higgs mass are more than difficult to reconcile with the strong constraints on the physical parameters of the Standard Model and the Minimal Supersymmetric Standard Model imposed by the preservation of the baryon asymmetry. This bound can be weakened by assuming a nonstandard cosmology at the time of the electroweak phase transition, reverting back to standard cosmology by BBN time. Two explicit examples are an early period of matter dominated expansion due to a heavy right handed neutrino (see-saw scale), or a nonstandard braneworld expansion.
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Bonnet, F., Hirsch, M., Ota, T., & Winter, W. (2012). Systematic study of the d=5 Weinberg operator at one-loop order. J. High Energy Phys., 07(7), 153–23pp.
Abstract: We perform a systematic study of the d = 5 Weinberg operator at the one-loop level. We identify three different categories of neutrino mass generation: (1) finite irreducible diagrams; (2) finite extensions of the usual seesaw mechanisms at one-loop and (3) divergent loop realizations of the seesaws. All radiative one-loop neutrino mass models must fall in to one of these classes. Case (1) gives the leading contribution to neutrino mass naturally and a classic example of this class is the Zee model. We demonstrate that in order to prevent that a tree level contribution dominates in case (2), Majorana fermions running in the loop and an additional Z(2) symmetry are needed for a genuinely leading one-loop contribution. In the type-II loop extensions, the Yukawa coupling will be generated at one loop, whereas the type-I/III extensions can be interpreted as loop-induced inverse or linear seesaw mechanisms. For the divergent diagrams in category (3), the tree level contribution cannot be avoided and is in fact needed as counter term to absorb the divergence.
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Donini, A., Hernandez, P., Lopez-Pavon, J., Maltoni, M., & Schwetz, T. (2012). The minimal 3+2 neutrino model versus oscillation anomalies. J. High Energy Phys., 07(7), 161–20pp.
Abstract: We study the constraints imposed by neutrino oscillation experiments on the minimal extension of the Standard Model that can explain neutrino masses, which requires the addition of just two singlet Weyl fermions. The most general renormalizable couplings of this model imply generically four massive neutrino mass eigenstates while one remains massless: it is therefore a minimal 3+2 model. The possibility to account for the confirmed solar, atmospheric and long-baseline oscillations, together with the LSND/MiniBooNE and reactor anomalies is addressed. We find that the minimal model can fit oscillation data including the anomalies better than the standard 3 nu model and similarly to the 3 + 2 phenomenological models, even though the number of free parameters is much smaller than in the latter. Accounting for the anomalies in the minimal model favours a normal hierarchy of the light states and requires a large reactor angle, in agreement with recent measurements. Our analysis of the model employs a new parametrization of seesaw models that extends the Casas-Ibarra one to regimes where higher order corrections in the light-heavy mixings are significant.
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Racker, J., Pena, M., & Rius, N. (2012). Leptogenesis with small violation of B – L. J. Cosmol. Astropart. Phys., 07(7), 030–18pp.
Abstract: We analyze leptogenesis in the context of seesaw models with almost conserved lepton number, focusing on the L-conserving contribution to the flavoured CP asymmetries. We find that, contrary to previous claims, successful leptogenesis is feasible for masses of the lightest heavy neutrino as low as M-1 similar to 10(6) GeV, without resorting to the resonant enhancement of the CP asymmetry for strongly degenerate heavy neutrinos. This lower limit renders thermal leptogenesis compatible with the gravitino bound in supersymmetric scenarios.
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del Aguila, F., Aparici, A., Bhattacharya, S., Santamaria, A., & Wudka, J. (2012). Effective Lagrangian approach to neutrinoless double beta decay and neutrino masses. J. High Energy Phys., 06(6), 146–37pp.
Abstract: Neutrinoless double beta (0 nu beta beta) decay can in general produce electrons of either chirality, in contrast with the minimal Standard Model (SM) extension with only the addition of the Weinberg operator, which predicts two left-handed electrons in the final state. We classify the lepton number violating (LNV) effective operators with two leptons of either chirality but no quarks, ordered according to the magnitude of their contribution to 0 nu beta beta decay. We point out that, for each of the three chirality assignments, e(L)e(L), e(L)e(R) and e(R)e(R), there is only one LNV operator of the corresponding type to lowest order, and these have dimensions 5, 7 and 9, respectively. Neutrino masses are always induced by these extra operators but can be delayed to one or two loops, depending on the number of RH leptons entering in the operator. Then, the comparison of the 0 nu beta beta decay rate and neutrino masses should indicate the effective scenario at work, which confronted with the LHC searches should also eventually decide on the specific model elected by nature. We also list the SM additions generating these operators upon integration of the heavy modes, and discuss simple realistic examples of renormalizable theories for each case.
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ANTARES Collaboration(Adrian-Martinez, S. et al), Bigongiari, C., Dornic, D., Emanuele, U., Gomez-Gonzalez, J. P., Hernandez-Rey, J. J., et al. (2012). Measurement of atmospheric neutrino oscillations with the ANTARES neutrino telescope. Phys. Lett. B, 714(2-5), 224–230.
Abstract: The data taken with the ANTARES neutrino telescope from 2007 to 2010, a total live time of 863 days, are used to measure the oscillation parameters of atmospheric neutrinos. Muon tracks are reconstructed with energies as low as 20 GeV. Neutrino oscillations will cause a suppression of vertical upgoing muon neutrinos of such energies crossing the Earth. The parameters determining the oscillation of atmospheric neutrinos are extracted by fitting the event rate as a function of the ratio of the estimated neutrino energy and reconstructed flight path through the Earth. Measurement contours of the oscillation parameters in a two-flavour approximation are derived. Assuming maximal mixing, a mass difference of Delta m(32)(2) = (3.1 +/- 0.9) . 10(-3) eV(2) is obtained, in good agreement with the world average value.
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ANTARES Collaboration(Adrian-Martinez, S. et al), Bigongiari, C., Dornic, D., Emanuele, U., Gomez-Gonzalez, J. P., Hernandez-Rey, J. J., et al. (2012). Search for neutrino emission from gamma-ray flaring blazars with the ANTARES telescope. Astropart Phys., 36(1), 204–210.
Abstract: The ANTARES telescope is well-suited to detect neutrinos produced in astrophysical transient sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. Radio-loud active galactic nuclei with jets pointing almost directly towards the observer, the so-called blazars, are particularly attractive potential neutrino point sources. The all-sky monitor LAT on board the Fermi satellite probes the variability of any given gamma-ray bright blazar in the sky on time scales of hours to months. Assuming hadronic models, a strong correlation between the gamma-ray and the neutrino fluxes is expected. Selecting a narrow time window on the assumed neutrino production period can significantly reduce the background. An unbinned method based on the minimization of a likelihood ratio was applied to a subsample of data collected in 2008 (61 days live time). By searching for neutrinos during the high state periods of the AGN light curve, the sensitivity to these sources was improved by about a factor of two with respect to a standard time-integrated point source search. First results on the search for neutrinos associated with ten bright and variable Fermi sources are presented.
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