Neutrino Flux Ratio Research Articles

Quantum gravitational decoherence in the three neutrino flavor scheme

In many theories of quantum gravity quantum fluctuations of spacetime may serve as an environment for decoherence. Here we study quantum-gravitational decoherence of high-energy astrophysical neutrinos in the presence of fermionic dark sectors and for a realistic three neutrino scenario. We show how violation of global symmetries expected to arise in quantum gravitational interactions provides a possibility to pin down the number of dark matter fermions in the Universe. Furthermore, we predict the expected total neutrino flux and flavor ratios at experiments depending on the flavor composition at the source.

A study on a minimally broken residual TBM-Klein symmetry with its implications on flavoured leptogenesis and ultra high energy neutrino flux ratios

We present a systematic study on minimally perturbed neutrino mass matrices which at the leading order give rise to Tri-BiMaximal (TBM) mixing due to a residual ℤ2× ℤ2μτ Klein symmetry in the neutrino mass term of the low energy effective seesaw Lagrangian. Considering only the breaking of ℤ2μτ with two relevant breaking parameters (ϵ4,6′), after a comprehensive numerical analysis, we show that the phenomenologically viable case in this scenario is a special case of TM1 mixing. For this class of models, from the phenomenological perspective, one always needs large breaking (more than 45%) in one of the breaking parameters. However, to be consistent the maximal mixing of θ23, while more than 35% breaking is needed in the other, a range 49.4̂−53̂ and 38̂−40̂ could be probed allowing breaking up to 25% in the same parameter. Thus though this model cannot distinguish the octant of θ23, non-maximal mixing is preferred from the viewpoint of small breaking. The full ℤ2× ℤ2μτ symmetry leads to a degeneracy in the eigenvalues of right handed (RH) neutrino mass matrices (MR). Nevertheless, breaking of ℤ2μτ which is also necessary to generate nonzero θ13 in this model, lifts that degeneracy. Thus unlike the standard N1-leptogenesis scenario where only the decays and other interactions due to the lightest RH neutrino N1 are relevant, here all the RH neutrinos contribute to the process of baryogenesis via leptogenesis due to the small mass splitting controlled by the ℤ2μτ breaking parameters. Including flavour coupling effects (In general, which have been partially included in all the leptogenesis studies in perturbed TBM framework), we solve flavour dependent coupled Boltzmann equations for heavy neutrino as well as the light leptonic number densities to compute the final baryon asymmetry YB. Thus our analysis and results pertaining to a successful leptogenesis are more accurate than any other studies in existing literature that deal with perturbed TBM scenario. Finally, in the context of recent discovery of the ultra high energy (UHE) neutrino events at IceCube, assuming UHE neutrinos originate from purely astrophysical sources, we obtain prediction on the neutrino flux ratios at neutrino telescopes.

Influence of hadronic interaction models on characteristics of the high-energy atmospheric neutrino flux

The high-energy conventional atmospheric neutrino fluxes are calculated with the hadronic interaction models: Kimel & Mokhov, QGSJET II-03(04), SIBYL 2.1(2.3), EPOS LHC. The influence of hadron-nuclear interactions on the neutrino flux ratios, , is studied. A comparison of calculations obtained with use of two different approaches, -functions method and the Matrix Cascade Equations (MCEQ), demonstrates close agreement in whole but some of partial contrubutions. The comparison of calculated muon neutrino spectra with the latest experimental data justifies reliability of performed computation which describes correctly the atmospheric neutrino production. The calculation made with the model EPOS LHC, combined with Hillas & Gaisser parametrization of the cosmic ray spectrum, is in close agreement with the best fit of IceCube for energy spetrum of atmospheric muon neutrinos in the energy range 1–500 TeV.

Using the standard solar model to constrain solar composition and nuclear reactionSfactors

While standard solar model (SSM) predictions depend on approximately 20 input parameters, SSM neutrino flux predictions are strongly correlated with a single model output parameter, the core temperature $T_c$. Consequently, one can extract physics from solar neutrino flux measurements while minimizing the consequences of SSM uncertainties, by studying flux ratios with appropriate power-law weightings tuned to cancel this $T_c$ dependence. We re-examine an idea for constraining the primordial C+N content of the solar core from a ratio of CN-cycle $^{15}$O to pp-chain $^8$B neutrino fluxes, showing that nonnuclear SSM uncertainties in the ratio are small and effectively governed by a single parameter, the diffusion coefficient. We point out that measurements of both CN-I cycle neutrino branches -- $^{15}$O and $^{13}$N $\beta$-decay -- could in principle lead to separate determinations of the core C and N abundances, due to out-of-equilibrium CN-cycle burning in the cooler outer layers of the solar core. Finally, we show that the strategy of constructing "minimum uncertainty" neutrino flux ratios can also test other properties of the SSM. In particular, we demonstrate that a weighted ratio of $^7$Be and $^8$B fluxes constrains a product of S-factors to the same precision currently possible with laboratory data.

LeptonicCPviolation at neutrino telescopes

With the advent of the recent measurements in neutrino physics, we investigate the role of high-energy neutrino flux ratios at neutrino telescopes for the possibility of determining the leptonic CP-violating phase \delta and the underlying pattern of the leptonic mixing matrix. We find that the flux ratios show a dependence of O(10 %) on the CP-violating phase, and for optimistic uncertainties on the flux ratios less than 10 %, they can be used to distinguish between CP-conserving and CP-violating values of the phase at 2\sigma in a non-vanishing interval around the maximal value |\delta|=\pi/2.

Neutrino flavor ratio on Earth and at astrophysical sources

We present the reconstruction of neutrino flavor ratios at astrophysical sources. For distinguishing the pion source and the muon-damped source to the 3 σ level, the neutrino flux ratios, R ≡ ϕ ( ν μ ) / ( ϕ ( ν e ) + ϕ ( ν τ ) ) and S ≡ ϕ ( ν e ) / ( ϕ ( ν τ ) ) , need to be measured in accuracies better than 10%.

Neutrino flux ratios at neutrino telescopes: The role of uncertainties of neutrino mixing parameters and applications to neutrino decay

In this paper, we derive simple and general perturbative formulas for the flavor flux ratios ${R}_{\ensuremath{\alpha}\ensuremath{\beta}}={\ensuremath{\phi}}_{{\ensuremath{\nu}}_{\ensuremath{\alpha}}}/{\ensuremath{\phi}}_{{\ensuremath{\nu}}_{\ensuremath{\beta}}}$ that could be measured at neutrino telescopes. We discuss in detail the role of the uncertainties of the neutrino mixing parameters showing that they have to be seriously taken into account in any realistic discussion about flavor measurements at neutrino telescopes. In addition, we analyze the impact of such uncertainties in telling the standard neutrino oscillation framework from scenarios involving, e.g., neutrino decay and we find that the ratio ${R}_{e\ensuremath{\mu}}$ is the most sensitive one to ``new physics'' effects beyond the standard model. We also compute the more realistic muon-to-shower ratio for a particular configuration of the IceCube experiment, observing that using this experimental quantity a clear separation between standard and nonstandard neutrino physics cannot be obtained.

LS I +61 303 as a potential neutrino source on the light of magic results

Very high energy γ-rays have recently been detected from the microquasar LS I +61 303 using the MAGIC telescope. A phenomenological study on the concomitant neutrinos that would be radiated if the γ-ray emission is hadronic in origin is herein presented. Neutrino oscillations are considered, and the expected number of events in a km-scale detector such as ICECUBE is computed under different assumptions including orbital periodicity and modulation, as well as different precision in the modeling of the detector. We argue that the upper limits already imposed on the neutrino emission of LS I +61 303 using AMANDA-II and the forthcoming measurements by ICECUBE may significantly constrain – in an independent and unbiased way – the γ-ray to neutrino flux ratio, and thus the possibility of a hadronic origin of the γ-rays. The viability of hadronic models based on wind–jet interactions in the LS +61 303 system after MAGIC measurements is discussed.

Determination of the initial flavor composition of ultrahigh-energy neutrino fluxes with neutrino telescopes

We propose a simple but useful parametrization of the flavor composition of ultrahigh-energy neutrino fluxes produced from distant astrophysical sources: ${\ensuremath{\phi}}_{e}\ensuremath{\mathbin:}{\ensuremath{\phi}}_{\ensuremath{\mu}}\ensuremath{\mathbin:}{\ensuremath{\phi}}_{\ensuremath{\tau}}={sin}^{2}\ensuremath{\xi}{cos}^{2}\ensuremath{\zeta}\ensuremath{\mathbin:}{cos}^{2}\ensuremath{\xi}{cos}^{2}\ensuremath{\zeta}\ensuremath{\mathbin:}{sin}^{2}\ensuremath{\zeta}$. We show that it is possible to determine or constrain $\ensuremath{\xi}$ and $\ensuremath{\zeta}$ by observing two independent neutrino flux ratios at the second-generation neutrino telescopes, provided three neutrino mixing angles and the Dirac $CP$-violating phase have been well measured in neutrino oscillations. Any deviation of $\ensuremath{\zeta}$ from zero will signify the existence of cosmic ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ and ${\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ neutrinos at the source, and an accurate value of $\ensuremath{\xi}$ can be used to test both the conventional mechanism and the postulated scenarios for cosmic neutrino production.

STANDARD AND NON-STANDARD SOLAR MODELS

We summarize the physical input and assumptions commonly adopted in modern standard solar models that also produce good agreement with solar oscillation frequencies. We discuss two motivations for considering non-standard models: the solar neutrino problem and surface lithium abundance problem. We begin to explore the potential for mixed core models to solve the neutrino problem, and compare the structure, neutrino flux, and oscillation frequency predictions for several models in which the inner 25% of the radius is homogenized, taking into account the effects of non-local equilibrium abundances of 3He. The results for the neutrino flux and helioseismic predictions are far from satisfactory, but such models have the potential to reduce the predicted 7Be/8B neutrino flux ratio, and further studies are warranted. Finally, we discuss how much the neutrino problem can be alleviated in the framework of the standard solar model by using reaction rates, abundances and neutrino capture cross-sections at the limits of their uncertainties, while still satisfying the constraints of helioseismology.

Effects of neutrino mixing on high-energy cosmic neutrino flux

Several cosmologically distant astrophysical sources may produce high-energy cosmic neutrinos $(Eg~{10}^{6}$ GeV) of all flavors above the atmospheric neutrino background. We study the effects of vacuum neutrino mixing in the three flavor framework on this cosmic neutrino flux. We also consider the effects of possible mixing between the three active neutrinos and the (fourth) sterile neutrino with or without big-bang nucleosynthesis constraints and estimate the resulting final high-energy cosmic neutrino flux ratios on Earth compatible with currently existing different neutrino oscillation hints in a model independent way. Further, we discuss the case where the intrinsic cosmic neutrino flux does not have the standard ratio.

Prospects for observations of high-energy cosmic tau neutrinos

We study the prospects for the observation of high-energy cosmic tau neutrinos $(E>~{10}^{6}$ GeV) originating from proton acceleration in the cores of active galactic nuclei. We consider the possibility that vacuum flavor neutrino oscillations induce a tau to muon neutrino flux ratio greatly exceeding the rather small value expected from intrinsic production. The criteria and event rates for under water or ice light \ifmmode \check{C}\else \v{C}\fi{}erenkov neutrino telescopes are given by considering the possible detection of downgoing high-energy cosmic tau neutrinos through characteristic double shower events.

Solar neutrino results from Super-Kamiokande

The recent results from the solar neutrino observation in Super-Kamiokande is presented. From the 504 days of data, taken between the 31st of May, 1996 and the 25th of March, 1998, we have obtained the 8B-solar neutrino flux ratio to the prediction of the standard solar model of BP98 to be 0.474 −0.009 −0.014 +0.010 +0.017 (0.506 −0.010 −0.015 +0.011 +0.018 for TC98). We found no significant difference between day and nighttime flux. The spectrum shape is compared with the expected from the 8B-neutrino spectrum, the neutrino interaction and the detector response, and we have obtained χ 2 of 25.3 (15 d.o.f), corresponding to a 4.6% C.L. Implications of these measurements to neutrino oscillations are discussed.

Seismic Tests of the Sun's Interior Structure, Composition, and Age, and Implications for Solar Neutrinos

The structure of the deep interior of a variety of standard and nonstandard solar models constrained by the low-l p-mode oscillation data from GONG are presented. For standard models, we show that the effects of both helium and heavy-element diffusion must be included in order to find simultaneous agreement with both the p-mode spectrum and the observed value of (Z/X)☉. Related to this conclusion, we find that the average interior heavy-element abundance is greater than the observed surface abundance in models whose small spacings, which are derived from the p-mode oscillation spectra, best match the observations. The high-quality data from the Global Oscillation Network Group (GONG) now permit a precise determination of the seismic age of the Sun. The best agreement with the calculated oscillation spectra is achieved for 4.5 ± 0.1 Gyr, an age closely consistent with the age of the Sun inferred from meteorites, i.e., 4.53 ± 0.04 Gyr. This result lends strong support to the standard assumption of the theory of stellar evolution. With regard to the nonstandard solar models, we set limits on the extent to which the nonstandard assumptions can be applied to the model while still being consistent with the observed p-modes. The nonstandard assumptions investigated here are: forced mixing in the core, forced mixing in a shell surrounding the core, and near-zero heavy-element abundance in the core. These assumptions were selected because at one time or another they have all been proposed to reduce the neutrino flux of the solar model, thereby bringing the flux of the model more in line with the observed flux. All nonstandard models include helium and heavy element diffusion. We confirm, now using the latest solar model physics, that these nonstandard assumptions, when capable of reducing significantly the solar neutrino flux, perturb the interior structure too much to be consistent with p-mode observations. In addition, we set strict limits on the extent to which these nonstandard assumptions are tolerated by the current p-mode observations. For example, we show that the p-mode small spacings are incompatible with a low-Z core larger than 0.06 M☉ in the Sun. And we show that if the Sun's core is chemically mixed, the extent of the mixed core cannot exceed 0.02 M☉. The seismic data are also incompatible with extensive rapid mixing of 4He in the solar envelope. This, we believe, also argues against the possibility of slow mixing of 3He occurring in a shell, as was recently proposed by Cumming and Haxton to lower the 7Be/8B neutrino flux ratio. But we note that the occurrence of some mixing of 3He and other trace elements and isotopes in the region of the solar interior where the initial 4He abundance is nearly uniform (which could not at this point be detected by seismology) might modify the calculated neutrino fluxes.

3He Transport in the Sun and the Solar Neutrino Problem.

Recent solar neutrino experiments show that both $\ensuremath{\varphi}{(}^{8}\mathrm{B})$ and the neutrino flux ratio $\ensuremath{\varphi}{(}^{7}\mathrm{Be})/\ensuremath{\varphi}{(}^{8}\mathrm{B})$ are substantially below their standard solar model values, leading some to discount the possibility of an astrophysical solution to the solar neutrino puzzle. We test this conclusion phenomenologically and find that the discrepancies can be significantly reduced by a distinctive pattern of core mixing on time scales characteristic of ${}^{3}\mathrm{He}$ equilibration.

Prompt neutrino results from a proton beam dump experiment

A study of prompt neutrino events from 400 GeV protons on a beam-dump is presented. The ratio of electron- to muon-neutrino rates is 0.86±0.14, in agreement withe−μ universality. The anti-neutrino to neutrino flux ratio is $$\bar v_\mu /v_\mu = 0.81 \pm 0.19$$ . The absolute rates and distributions observed are shown to be in quantitative agreement with the known properties of charmedquark production in hadron collisions.