Non-standard Neutrino Properties Research Articles

Probing neutrino decay scenarios by using the Earth matter effects on supernova neutrinos

The observation of Earth matter effects in the spectrum of neutrinos coming from a next galactic core-collapse supernova (CCSN) could, in principle, reveal if neutrino mass ordering is normal or inverted. One of the possible ways to identify the mass ordering is through the observation of the modulations that appear in the spectrum when neutrinos travel through the Earth before they arrive at the detector. These features in the neutrino spectrum depend on two factors, the average neutrino energies, and the difference between the primary neutrino fluxes of electron and other flavors produced inside the supernova. However, recent studies indicate that the Earth matter effect for CCSN neutrinos is expected to be rather small and difficult to be observed by currently operating or planned neutrino detectors mainly because of the similarity of average energies and fluxes between electron and other flavors of neutrinos, unless the distance to CCSN is significantly smaller than the typically expected one, ∼ 10 kpc. Here, we are looking towards the possibility if the non-standard neutrino properties such as decay of neutrinos can enhance the Earth matter effect. In this work we show that invisible neutrino decay can potentially enhance significantly the Earth matter effect for both νe and ν̅e channels at the same time for both mass orderings, even if the neutrino spectra between electron and other flavors of neutrinos are very similar, which is a different feature not expected for CCSN neutrinos with standard oscillation without the decay effect.

Calorimetric method for determination of 51Cr neutrino source activity

Experimental study of nonstandard neutrino properties using high-intensity artificial neutrino sources requires the activity of the sources to be determined with high accuracy. In the BEST project, a calorimetric system for measurement of the activity of high-intensity (a few MCi) neutrino sources based on 51Cr with an accuracy of 0.5–1% is created. In the paper, the main factors affecting the accuracy of determining the neutrino source activity are discussed. The calorimetric system design and the calibration results using a thermal simulator of the source are presented.

Flavor ratios of extragalactic neutrinos and neutrino shortcuts in extra dimensions

The recent measurement of high energy extragalactic neutrinos by the IceCube Collaboration has opened a new window to probe non-standard neutrino properties. Among other effects, sterile neutrino altered dispersion relations (ADRs) due to shortcuts in an extra dimension can significantly affect astrophysical flavor ratios. We discuss two limiting cases of this effect, first active-sterile neutrino oscillations with a constant ADR potential and second an MSW-like resonant conversion arising from geodesics oscillating around the brane in an asymmetrically warped extra dimension. We demonstrate that the second case has the potential to suppress significantly the flux of specific flavors such as νμ or ντ at high energies.

The power spectrum and bispectrum of SDSS DR11 BOSS galaxies – II. Cosmological interpretation

We examine the cosmological implications of the measurements of the linear growth rate of cosmological structure obtained in a companion paper from the power spectrum and bispectrum monopoles of the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey Data, Release 11, CMASS galaxies. This measurement was of $f^{0.43}\sigma_8$, where $\sigma_8$ is the amplitude of dark matter density fluctuations, and $f$ is the linear growth rate, at the effective redshift of the survey, $z_{\rm eff}=0.57$. In conjunction with Cosmic Microwave Background (CMB) data, interesting constraints can be placed on models with non-standard neutrino properties and models where gravity deviates from general relativity on cosmological scales. In particular, the sum of the masses of the three species of the neutrinos is constrained to $m_\nu<0.49\,{\rm eV}$ (at 95\% confidence level) when the $f^{0.43}\sigma_8$ measurement is combined with state-of-the-art CMB measurements. Allowing the effective number of neutrinos to vary as a free parameter does not significantly change these results. When we combine the measurement of $f^{0.43}\sigma_8$ with the complementary measurement of $f\sigma_8$ from the monopole and quadrupole of the two-point correlation function we are able to obtain an independent measurements of $f$ and $\sigma_8$. We obtain $f=0.63\pm0.16$ and $\sigma_8=0.710\pm0.086$ (68\% confidence level). This is the first time when these parameters have been able to be measured independently using the redshift-space power spectrum and bispectrum measurements from galaxy clustering data only.

Neutrino anisotropies after Planck

We present new constraints on the rest-frame sound speed, c_{eff}^2, and the viscosity parameter, c_{vis}^2, of the Cosmic Neutrino Background from the recent measurements of the Cosmic Microwave Background anisotropies provided by the Planck satellite. While broadly consistent with the expectations of c_{eff}^2=c_{vis}^2=1/3 in the standard scenario, the Planck dataset hints at a higher value of the viscosity parameter, with c_{vis}^2=0.60+/-0.18 at 68% c.l., and a lower value of the sound speed, with c_{eff}^2=0.304+/-0.013 at 68% c.l.. We find a correlation between the neutrino parameters and the lensing amplitude of the temperature power spectrum A_L. When the latter parameter is allowed to vary, we find a better consistency with the standard model with c_{vis}^2=0.51+/-0.22, c_{eff}^2=0.311+/-0.019 and A_L=1.08+/-0.18 at 68% c.l.. This result indicates that the anomalous large value of A_L measured by Planck could be connected to non-standard neutrino properties. Including additional datasets from Baryon Acoustic Oscillation surveys and the Hubble Space Telescope constraint on the Hubble constant, we obtain c_{vis}^2=0.40+/-0.19, c_{eff}^2=0.319+/-0.019, and A_{L}=1.15+/-0.17 at 68% c.l.; including the lensing power spectrum, we obtain c_{vis}^2=0.50+/-0.19, c_{eff}^2=0.314+/-0.015, and A_L=1.025+/-0.076 at 68% c.l.. Finally, we investigate further degeneracies between the clustering parameters and other cosmological parameters.

Particle-physics constraints from the globular cluster M5: neutrino dipole moments

Stellar evolution is modified if energy is lost in a "dark channel" similar to neutrino emission. Comparing modified stellar evolution sequences with observations provides some of the most restrictive limits on axions and other hypothetical low-mass particles and on non-standard neutrino properties. In particular, a putative neutrino magnetic dipole moment mu_nu enhances the plasmon decay process, postpones helium ignition in low-mass stars, and therefore extends the red-giant branch (RGB) in globular clusters (GCs). The brightness of the tip of the RGB (TRGB) remains the most sensitive probe for mu_nu and we revisit this argument from a modern perspective. Based on a large set of archival observations, we provide high-precision photometry for the Galactic GC M5 (NGC5904) and carefully determine its TRGB position. On the theoretical side, we add the extra plasmon decay rate brought about by mu_nu to the Princeton-Goddard-PUC stellar evolution code. Different sources of uncertainty are critically examined. The main source of systematic uncertainty is the bolometric correction and the main statistical uncertainty derives from the distance modulus based on main-sequence fitting. (Other measures of distance, e.g., the brightness of RR Lyrae stars, are influenced by the energy loss that we wish to constrain.) The statistical uncertainty of the TRGB position relative to the brightest RGB star is less important because the RGB is well populated. We infer an absolute I-band brightness of M_I=-4.17+/-0.13 mag for the TRGB compared with the theoretical prediction of -3.99+/-0.07 mag, in reasonable agreement with each other. A significant brightness increase caused by neutrino dipole moments is constrained such that mu_nu<2.6x10^-12mu_B(68% CL), where mu_B is the Bohr magneton, and mu_nu<4.5x10^-12 mu_B(95% CL). In these results, statistical and systematic errors have been combined in quadrature.

Is there evidence for additional neutrino species from cosmology?

It has been suggested that recent cosmological and flavor-oscillation data favor the existence of additional neutrino species beyond the three predicted by the Standard Model of particle physics. We apply Bayesian model selection to determine whether there is indeed any evidence from current cosmological datasets for the standard cosmological model to be extended to include additional neutrino flavors. The datasets employed include cosmic microwave background temperature, polarization and lensing power spectra, and measurements of the baryon acoustic oscillation scale and the Hubble constant. We also consider other extensions to the standard neutrino model, such as massive neutrinos, and possible degeneracies with other cosmological parameters. The Bayesian evidence indicates that current cosmological data do not require any non-standard neutrino properties.

Testing nonstandard neutrino properties with a Mössbauer oscillation experiment

If the neutrino analogue of the M\"ossbauer effect, namely, recoiless emission and resonant capture of neutrinos is realized, one can study neutrino oscillations with much shorter baselines and smaller source/detector size when compared to conventional experiments. In this work, we discuss the potential of such a M\"ossbauer neutrino oscillation experiment to probe nonstandard neutrino properties coming from some new physics beyond the standard model. We investigate four scenarios for such new physics that modify the standard oscillation pattern. We consider the existence of a light sterile neutrino that can mix with \bar \nu_e, the existence of a Kaluza-Klein tower of sterile neutrinos that can mix with the flavor neutrinos in a model with large flat extra dimensions, neutrino oscillations with nonstandard quantum decoherence and mass varying neutrinos, and discuss to which extent one can constrain these scenarios. We also discuss the impact of such new physics on the determination of the standard oscillation parameters.

Neutrinos in astrophysics and cosmology

Nonstandard neutrino properties (masses, mixing, sterile states, electromagnetic interactions, and so forth) can have far-reaching ramifications in astrophysics and cosmology. We look at the most interesting cases in the light of the powerful current indications for neutrino oscillations.

Test of non-standard neutrino properties with the BOREXINO source experiments

We calculate the event rates induced by high-intensity radioactive sources of nu_e (51Cr) and of anti-nu_e (90Sr), to be located near the BOREXINO detector. Calculations are performed both in the standard case and assuming non-standard properties of neutrinos, including flavor oscillations, neutrino electromagnetic interactions, and deviations from the standard vector and axial couplings in the nu_e-e interaction. It is shown that, in some cases, the current limits on non-standard neutrino properties can be significantly improved.

Test of non-standard neutrino properties with the BOREXINO source experiments

Test of non-standard neutrino properties with the BOREXINO source experiments

Solar neutrino spectroscopy

Since the pioneering experiment of R. Davis et al., which started neutrino astronomy by measuring the solar neutrinos via the inverse beta decay reaction on 37Cl, all solar neutrino experiments find a considerably lower flux than expected by standard solar models. This finding is generally called the solar neutrino problem. Many attempts have been made to explain this result by altering the solar models, or assuming different nuclear cross sections for fusion processes assumed to be the energy sources in the sun. There have been performed numerous experiments recently to investigate the different possibilities to explain the solar neutrino problem. These experiments covered solar physics with helioseismology, nuclear cross section measurements, and solar neutrino experiments. Up to now no convincing explanation based on “standard” physics was suggested. However, assuming nonstandard neutrino properties, i.e. neutrino masses and mixing as expected in most extensions of the standard theory of elementary particle physics, natural solutions for the solar neutrino problem can be found. It appears that with this newly invented neutrino astronomy fundamental information on astrophysics as well as elementary particle physics are tested uniquely. In this contribution an attempt is made to review the situation of the neutrino astronomy for solar neutrino spectroscopy and discuss the future prospects in this field.

Neutrino magnetic moments and low-energy solar neutrino-electron scattering experiments

The scattering of solar neutrinos on electrons is sensitive to the neutrino magnetic moments through an interference of electromagnetic and weak amplitudes in the cross section. We show that future low-energy solar neutrino experiments with good angular resolution can be sensitive to the resulting azimuthal asymmetries in event number and should provide useful information on non-standard neutrino properties such as magnetic moments. We compare asymmetries expected at Hellaz (mainly $\mathrm{pp}$ neutrinos) with those at the Kamiokande and Super-Kamiokande experiments (boron neutrinos), both for the case of Dirac and Majorana neutrinos and discuss the advantages of low energy experiments. Potentially interesting information on the solar magnetic fields may be accessible.

Future solar neutrino spectroscopy and neutrino properties

The GALLEX result, together with the constraints from the observed value o f the solar constant, yields strong limits on the flux of neutrinos from the pp-I termination of the pp-chain, 62⩽ φ pp+pep [10 9 cm −2 s −1] ⩽65 , provided that neutrinos are standard. This conclusion is essentially independent of solar models and it implies that the pp-chain is shifted towards the pp-I termination, in comparison with the SSM predictions. As a consequence, we derive an upper bound on Berillium neutrinos: φ Be⩽3×10 9 cm −2 s −1, the violation of this bound being a clear signal of non-standard neutrino properties. We also find that, for a large class of solar models built so as to enhance the pp-I termination, the pep-neutrino flux is stable around φ pep ≈ 1.5×10 8 cm −2 s −1. Detection of pep neutrinos will clearly discriminate standard neutrinos against MSW oscillations, this latter model giving φ MSW pep ⩽3×10 7 cm −2 s −1.

RECENT SOLAR NEUTRINO OBSERVATIONS AND RESONANT NEUTRINO MIXING

The results of recent data from the 37 Cl , Kamiokande-II (K-II) and 71 Ga solar neutrino experiments are quantitatively analyzed. The results suggest that non-standard neutrino properties, instead of a non-standard solar model, are the correct explanation for the "solar neutrino problem." Assuming resonant neutrino oscillations, it is found that the "non-adiabatic" and "large angle" solutions are in quite good agreement with the data. The implications of these solutions for forthcoming solar neutrino experiments are discussed.