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O. L. G. Peres

Publications and source records attributed to O. L. G. Peres.

At least 37 records · Page 2Linked to original sources
arXiv2014

Constraining the Violation of Equivalence Principle with IceCube Atmospheric Neutrino Data

The recent high-statistics high-energy atmospheric neutrino data collected by IceCube open a new window to probe new physics scenarios that are suppressed in lower energy neutrino experiments. In this paper we analyze the IceCube atmospheric neutrino data to constrain the Violation of Equivalence Principle (VEP) in the framework of three neutrinos with non-universal gravitational couplings. In this scenario the effect of VEP on neutrino oscillation probabilities can be parametrized by two parameters $Δγ_{21}\equiv γ_2-γ_1$ and $Δγ_{31}\equiv γ_3-γ_1$, where $γ_i$'s denote the coupling of neutrino mass eigenstates to gravitational field. By analyzing the latest muon-tracks data sets of IceCube-40 and IceCube-79, besides providing the 2D allowed regions in $(ϕΔγ_{21},ϕΔγ_{31})$ plane, we obtain the upper limits $|ϕΔγ_{21}| < 9.1\times 10^{-27}$ (at 90\% C.L.) which improves the previous limit by $\sim4$ orders of magnitude and $|ϕΔγ_{31}| \lesssim 6\times 10^{-27}$ (at 90\% C.L.) which improves the current limit by $\sim1$ order of magnitude. Also we discuss in detail and analytically the effect of VEP on neutrino oscillation probabilities.

hep-ph↗
arXiv2014

Impact of sterile neutrinos on the early time flux from a galactic supernova

We study the impact of the existence of an eV-mass scale sterile neutrino---with parameters in the ballpark of what is required to fit the laboratory anomalies---on the early time profile of the electron neutrino and antineutrino fluxes associated to a core-collapse supernova (SN). In particular, we focus on the universal feature of neutronization burst expected in the first tens of ms of the signal: provided that a detector with sufficient sensitivity is available, it is well-known that in the 3 neutrino framework the detection of the neutronization burst in neutrino channel would signal inverted mass hierarchy. This conclusion is dramatically altered in the presence of a sterile neutrino: we study here both analytically and numerically the region in parameter space where this characteristic signal disappears, mimicking normal hierarchy expectations. Conversely, the detection of a peak consistent with expectations for inverted mass hierarchy would exclude the existence of a sterile state over a much wider parameter space than what required by laboratory anomalies fits, or even probed by detectors coming on-line in the near future. Additionally, we show the peculiar alteration in the energy-time double differential flux, with a delayed peak appearing for kinematical reasons, which might offer a remarkable signature in case of favorable parameters and for a high statistics detection of a Galactic SN. We also comment on additional potentially interesting effects in the electron antineutrino channel, if more than one angle in the active-sterile sector is non-vanishing. As an ancillary result that we derived in the technical resolution of the equations, in an appendix we report the Cayley-Hamilton formalism for the evolution of a four neutrino system in matter, generalizing existing results in the literature.

hep-ph↗
arXiv2014

Searching for non-diagonal Mass varying mechanism in the $ν_μ$-$ν_τ$ system

We use atmospheric neutrino data and MINOS data to constrain the MaVaN (Mass Varying Neutrinos) mechanism. The MaVaN model was largely studied in cosmology scenarios and comes from the coupling of the neutrinos with a neutral scalar depending on the local matter density. For atmospheric neutrinos, this new interaction affects the neutrino propagation inside the Earth, and as consequence, induces modifications in their oscillation pattern. To perform such test for a non-standard oscillation mechanism with a non-diagonal neutrino coupling in the mass basis, we analyze the angular distribution of atmospheric neutrino events as seen by the Super-Kamiokande experiment for the events in the Sub-GeV and multi-GeV range and muon neutrinos (anti-neutrinos) in MINOS experiment. From the combined analysis of these two sets of data we obtain the best fit for $Δm^{2}_{32}=2.45 \times 10^{-3}$ eV$^{2}$, $sin^{2}(θ_{23})=0.42 $ and MaVaN parameter $α_{32}=0.28$ with modest improvement, $Δχ^{2}= 1.8$, over the standard oscillation scenario. The combination of MINOS data and Super-Kamiokande data prefers small values of MaVaN parameter $α_{32} < 0.31 $ at $90 \%$ C. L..

hep-ph↗
arXiv2014

Mass Varying Neutrinos in Supernovae

We study the consequences on the neutrino oscillation parameter space, mixing angle ($\tan^2θ$) and vacuum mass difference ($Δm^2_0$), when mass varying neutrino (MaVaN) models are assumed in a supernova environment. We consider electronic to sterile channels $ν_e \rightarrow ν_s$ and $\barν_e \rightarrow \barν_s$ in two-flavor scenario. In a given model of MaVaN mechanism, we induce a position-dependent effective mass difference, $Δ\tilde m^2(r)$, where $r$ is the distance from the supernova core, that changes the neutrino and anti-neutrino flavour conversion probabilities. We study the constraints on the mixing angle and vacuum mass difference coming from r-process and the SN1987A data. Our result is the appearance of a new exclusion region for very small mixing angles, $\tan^2θ=10^{-6}-10^{-2}$, and small vacuum mass difference, $Δm^2_0=~1-20$ eV$^2$, due the MaVaN mechanism.

hep-ph↗
arXiv2013

Probing light sterile neutrinos in medium baseline reactor experiments

Medium baseline reactor experiments (Double Chooz, Daya Bay and RENO) provide a unique opportunity to test the presence of light sterile neutrinos. We analyze the data of these experiments in the search of sterile neutrinos and also test the robustness of theta_13 determination in the presence of sterile neutrinos. We show that existence of a light sterile neutrino state improves the fit to these data moderately. We also show that the measured value of theta_{13} by these experiments is reliable even in the presence of sterile neutrinos, and the reliability owes significantly to the Daya Bay and RENO data. From the combined analysis of the data of these experiments we constrain the mixing of a sterile neutrino with mass squared difference in the range of (10^{-3}-10^{-1}) eV^2 to sin^2 2 theta_{14} <0.1 at 95 % C.L..

hep-ph↗
arXiv2013

Exploring ν_τ- ν_s mixing with cascade events in DeepCore

The atmospheric neutrino data collected by the IceCube experiment and its low-energy extension DeepCore provide a unique opportunity to probe the neutrino sector of the Standard Model. In the low energy range the experiment have observed neutrino oscillations, and the high energy data are especially sensitive to signatures of new physics in the neutrino sector. In this context, we previously demonstrated the unmatched potential of the experiment to reveal the existence of light sterile neutrinos. The studies are routinely performed in the simplest 3+1 model concentrating on disappearance of muon neutrinos of TeV energy as a result of their mixing with a sterile neutrino. We here extend this analysis to include cascade events that are secondary electromagnetic and hadronic showers produced by neutrinos of all flavors. We find that it is possible to probe the complete parameter space of 3+1 model, including the poorly constrained mixing of the sterile neutrino to tau neutrinos. We show that $ν_τ-ν_s$ mixing results into a unique signature in the data that will allow IceCube to obtain constraints well below the current upper limits.

hep-ph↗
arXiv2013

Stochastic Neutrino Mixing Mechanism

We propose a mechanism which provides an explanation of the Gallium and antineutrino reactor anomalies. Differently from original Pontecorvo's hypothesis, this mechanism is based on the phenomenological assumption in which the admixture of neutrino mass eigenstates in the moments of neutrino creation and detection can assume different configurations around the admixture parametrized by the usual values of the mixing angles $θ_{12}$, $θ_{23}$ and $θ_{13}$. For simplicity, we assume a Gaussian distribution for the mixing angles in such a way that the average value of this distribution is given by the usual values of the mixing angles and the width of the Gaussian is denoted by $α$. We show that the proposed mechanism provides a possible explanation for very short-baseline neutrino disappearance, necessary to accommodate Gallium and antineutrino reactor anomalies, which is not allowed in usual neutrino oscillations based on Pontecorvo's original hypotheses. We also can describe high-energy oscillation experiments, like LSND, Fermi and NuTeV, assuming a weakly energy dependent width parameter, $α(E)$, that nicely fits all experimental results.

hep-ph↗
arXiv2013

Constraining Sterile Neutrinos with AMANDA and IceCube Atmospheric Neutrino Data

We demonstrate that atmospheric neutrino data accumulated with the AMANDA and the partially deployed IceCube experiments constrain the allowed parameter space for a hypothesized fourth sterile neutrino beyond the reach of a combined analysis of all other experiments. We also illustrate the sensitivity of the completed IceCube detector, that is now taking data, to the parameter space of 3+1 model.

hep-ph↗
arXiv2009

Oscillations of very low energy atmospheric neutrinos

There are several new features in production, oscillations and detection of the atmospheric neutrinos of low energies, E<100 MeV. The flavor ratio, r, of muon to electron neutrino fluxes is substantially smaller than 2 and decreases with energy, significant part of events is due to the decay of invisible muons at rest, etc. Oscillations in two-layer medium (atmosphere - earth) should be taken into account. We derive analytical and semi-analytical expressions for the oscillation probabilities of these "sub-subGeV" neutrinos. The energy spectra of the e-like events in water cherenkov detectors are computed and dependence of the spectra on the 2-3 mixing angle, the 1-3 mixing and CP-violation phase are studied. We find that variations of 2-3 mixing angle in the presently allowed region change the number of e-like events by about 15 - 20 % as well as to distortion of the energy spectrum. The 1-3 mixing and CP-violation can lead to ~10% effects. Detailed study of the sub-subGeV neutrinos will be possible in future Megaton-scale detectors.

hep-ph↗
arXiv2007

Revising Limits on Neutrino-Majoron Couplings

Any theory that have a global spontaneously broken symmetry will imply the existence of very light neutral bosons or massless bosons (sometimes called Majorons). For most of these models we have neutrino-Majoron couplings, that appear as additional branching ratios in decays of mesons and leptons. Here we present an updated limits on the couplings between the electron, muon and tau neutrinos and Majorons. For such we analyze the possible effects of Majoron emission in both meson and lepton decays. In the latter we also include an analysis of the muon decay spectrum. Our results are $|g_{eα}|^{2}<5.5x10^{-6}$, $|g_{μα}|^{2}<4.5x10^{-5}$ and $|g_{τα}|^{2}<5.5x10^{-2}$ at 90 % C. L., where $α=e,μ,τ$.

hep-ph↗
arXiv2005

Angra Neutrino Project: status and plans

We present the status and plans of the Angra Project, a new nuclear reactor neutrino oscillation experiment, proposed to be built in Brazil at the Angra dos Reis nuclear reactor complex. This experiment is aimed to measure theta_13, the last unknown of the three neutrino mixing angles. Combining a high luminosity design, very low background from cosmic rays and careful control of systematic errors at the 1% level, we propose a high sensitivity multi-detector experiment, able to reach a sensitivity to antineutrino disappearance down to sin^2(2*theta_13) = 0.006 in a three years running period, improving present limits constrained by the CHOOZ experiment by more than an order of magnitude.

hep-ex↗
arXiv2005

Random magnetic fields inducing solar neutrino spin-flavor precession in a three generation context

We study the effect of random magnetic fields in the spin-flavor precession of solar neutrinos in a three generation context, when a non-vanishing transition magnetic moment is assumed. While this kind of precession is strongly constrained when the magnetic moment involves the first family, such constraints do not apply if we suppose a transition magnetic moment between the second and third families. In this scenario we can have a large non-electron anti-neutrino flux arriving on Earth, which can lead to some interesting phenomenological consequences, as, for instance, the suppression of day-night asymmetry. We have analyzed the high energy solar neutrino data and the KamLAND experiment to constrain the solar mixing angle, and solar mass difference, and we have found a larger shift of allowed values.

hep-ph↗
arXiv2004

Effects of non-standard neutrino interactions on MSW-LMA solution to the solar neutrino problem

We show that the non-standard neutrino interactions can play a role as sub-leading effect on the solar neutrino oscillations. We observe that very small flavor universality violations of order of 0.1-0.2 G_F is sufficient to induce two phenomena: suppression of the eletronic neutrino earth regeneration and a shift of the resonance layer in the sun. We obtain these phenomena even in the absence of any flavor changing interactions. We discuss their consequences and confront with a global analysis of solar+KamLAND results. We conclude that a new compatibility region in the Delta m^2 x tan^2θ, which we call very low Large Mixing Angle region, is found for Delta m^2 ~ 1e-5 eV^2 and tan^2θ= 0.45.

hep-ph↗
arXiv2003

Atmospheric neutrinos: LMA oscillations, Ue3 induced interference and CP-violation

We consider oscillations of the low energy (sub-GeV sample) atmospheric neutrinos in the three neutrino context. We present the semi-analytic study of the neutrino evolution and calculate characteristics of the e-like events (total number, energy spectra and zenith angle distributions) in the presence of oscillations. At low energies there are three different contributions to the number of events: the LMA contribution (from electron-neutrino oscillations driven by the solar oscillation parameters), the Ue3-contribution proportional to s13**2, and the Ue3 - induced interference of the two amplitudes driven by the solar oscillation parameters. The interference term is sensitive to the CP-violation phase. We describe in details properties of these contributions. We find that the LMA, the interference and Ue3 contributions can reach 5 - 6%, 2 - 3% and 1 - 2 % correspondingly. An existence of the significant (> 3 - 5 %) excess of the e-like events in the sub-GeV sample and the absence of the excess in the multi-GeV range testifies for deviation of the 2-3 mixing from maximum. We consider a possibility to measure the deviation as well as the CP- violation phase in future atmospheric neutrino studies.

hep-ph↗
arXiv2003

Probing the LSND scale and four neutrino scenarios with a neutrino telescope

We show in this paper that the observation of the angular distribution of upward-going muons and cascade events induced by atmospheric neutrinos at the TeV energy scale, which can be performed by a kilometer-scale neutrino telescope, such as the IceCube detector, can be used to probe a large neutrino mass splitting, $| Δm^2 | \sim (0.5-2.0)$ eV$^2$, implied by the LSND experiment and discriminate among four neutrino mass schemes. This is due to the fact that such a large mass scale can promote non negligible muon neutrino to electron/tau neutrino (and/or anti-muon neutrino to anti-electron/anti-tau neutrino) conversions at these energies by the MSW effect as well as vacuum oscillation, unlike what is expected if all the neutrino mass splittings are small.

hep-ph↗
arXiv2002

Measuring the Spectra of High Energy Neutrinos with a Kilometer-Scale Neutrino Telescope

We investigate the potential of a future kilometer-scale neutrino telescope such as the proposed IceCube detector in the South Pole, to measure and disentangle the yet unknown components of the cosmic neutrino flux, the prompt atmospheric neutrinos coming from the decay of charmed particles and the extra-galactic neutrinos, in the 10 TeV to 1 EeV energy range. Assuming a power law type spectra, $dϕ_ν/dE_ν\sim αE_ν^β$, we quantify the discriminating power of the IceCube detector and discuss how well we can determine magnitude ($α$) as well as slope ($β$) of these two components of the high energy neutrino spectrum, taking into account the background coming from the conventional atmospheric neutrinos.

hep-ph↗
arXiv2002

Global Analysis of the post-SNO Solar Neutrino Data for Standard and Non-Standard Oscillation Mechanisms

What can we learn from solar neutrino observations? Is there any solution to the solar neutrino anomaly which is favored by the present experimental panorama? After SNO results, is it possible to affirm that neutrinos have mass? In order to answer such questions we analyze the current available data from the solar neutrino experiments, including the recent SNO result, in view of many acceptable solutions to the solar neutrino problem based on different conversion mechanisms, for the first time, using the same statistical procedure. This allows us to do a direct comparison of the goodness of the fit among different solutions, from which we can discuss and conclude on the current status of each proposed dynamical mechanism. These solutions are based on different assumptions: (a) neutrino mass and mixing, (b) non-vanishing neutrino magnetic moment, (c) the existence of non-standard flavor-changing and non-universal neutrino interactions and (d) the tiny violation of the equivalence principle. We investigate the quality of the fit provided by each one of these solutions not only to the total rate measured by all the solar neutrino experiments but also to the recoil electron energy spectrum measured at different zenith angles by the Super-Kamiokande collaboration. We conclude that several non-standard neutrino flavor conversion mechanisms provide a very good fit to the experimental data which is comparable with (or even slightly better than) the most famous solution to the solar neutrino anomaly based on the neutrino oscillation induced by mass.

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