We consider a gauge model based on a SU(3)@U(1) symmetry in which the lepton number is violated explicitly by charged scalar and gauge bosons, including a vector field with double electric charge. PACS number(s): 12.15.Cc, 14.80.-j

We study the Glashow-Iliopoulos-Maiani mechanism for flavor-changing neutral-current suppression in both the gauge and Higgs sectors, for models with SU(3)z, Igt U(1)iv gauge symmetry. The models di6'er from one another only with respect to the representation content. The main features of these models are that in order to cancel the triangle anomalies the number of families must be divisible by three (the number of colors) and that the lepton number is violated by some lepton-gauge bosons and lepton-scalar interactions.

We consider an SU(3)r. @ U ( 1 ) p~ model for the electroweak interactions which includes extra charged leptons which do not mix with the known leptons. These new leptons couple to ZO only through vector currents. We consider constraints on the mass of one of these leptons coming from the Z0 width and from the muon ( g -2) factor. The last one is less restrictive than the former.

The SU(3) c ⊗SU(3) L ⊗U(1) N model of Pisano and Pleitez extends the Standard Model in a particularly nice way, so that for example the anomalies cancel only when the number of generations is divisible by three. The original version of the model has some problems accounting for the lepton masses. We resolve this problem by modifying the details of the symmetry breaking sector in the model.

Flavor changing (FC) neutrino-matter interactions can account for the zenith-angle-dependent deficit of atmospheric neutrinos observed in the SuperKamiokande experiment, without directly invoking either neutrino mass or mixing. We find that FC n m -matter interactions provide a good fit to the observed zenith angle distributions, comparable in quality to the neutrino oscillation hypothesis. The required FC interactions arise naturally in many attractive extensions of the standard model. [S0031-9007(99) PACS numbers: 14.60. Pq, 14.60.St, 25.30.Pt, 96.40.Tv Neutrinos produced as decay products in hadronic showers from cosmic ray collisions with nuclei in the upper atmosphere [1] have been observed by several detectors [2][3][4][5][6][7]. Although the absolute fluxes of atmospheric neutrinos are largely uncertain, the expected ratio ͑m͞e͒ of the muon neutrino flux ͑n m 1n m ͒ over the electron neutrino flux ͑n e 1n e ͒ is robust, since it largely cancels out the uncertainties associated with the absolute flux. In fact, this ratio has been calculated [1] with an uncertainty of less than 5% over energies varying from 0.1 to 100 GeV. In this resides our confidence in the longstanding atmospheric neutrino anomaly.Although the first iron-calorimeter detectors in Fréjus [2] and NUSEX [3] reported a value of the double ratio, R͑m͞e͒ ͑m͞e͒ data ͑͞m͞e͒ MC , consistent with one, all of the water Cherenkov detectors, Kamiokande [4], IMB [5], and SuperKamiokande [6], have measured R͑m͞e͒ significantly smaller than one. Moreover, not long ago, the Soudan-2 Collaboration, also using an iron calorimeter, reported a small value of R͑m͞e͒ [7], showing that the so-called atmospheric neutrino anomaly was not a feature of water Cherenkov detectors.Recent SuperKamiokande high statistics observations [6] indicate that the deficit in the total ratio R͑m͞e͒ is due to the number of neutrinos arriving in the detector at large zenith angles. Although e-like events do not present any compelling evidence of a zenith angle dependence, the m-like event rates are substantially suppressed at large zenith angles.The n m ! n t [6,8], as well as the n m ! n s [8,9], oscillation hypothesis provides an appealing explanation for this smaller-than-expected ratio, as they are simple and well motivated theoretically. This led the SuperKamiokande Collaboration to conclude that their data provide good evidence for neutrino oscillations and neutrino masses.In this Letter we give an alternative explanation of the atmospheric neutrino data in terms of flavor changing (FC) neutrino-matter interactions [10][11][12][13][14]. We show that, even if neutrinos have vanishing masses and/or the vacuum mixing angle is negligible, FC neutrino-matter interactions can still explain the SuperKamiokande data.There are attractive theories beyond the standard model (SM), where neutrinos are naturally massless [15] as a result of a protecting symmetry, such as B-L in the case of supersymmetric SU͑5͒ models [16] and the model proposed in [17], or chiral symmetry in theories w...