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A. Yu. Smirnov

Publications and source records attributed to A. Yu. Smirnov.

At least 109 records · Page 6Linked to original sources
arXiv2000

Phenomenology of Maximal and Near-Maximal Lepton Mixing

We study the phenomenological consequences of maximal and near-maximal mixing of the electron neutrino with other ($x$=tau and/or muon) neutrinos. We describe the deviations from maximal mixing in terms of a parameter $ε\equiv1-2\sin^2θ_{ex}$ and quantify the present experimental status for $|ε|<0.3$. We find that the global analysis of solar neutrino data allows maximal mixing with confidence level better than 99% for $10^{-8}$ eV$^2\lsimΔm^2\lsim2\times10^{-7}$ eV$^2$. In the mass ranges $Δm^2\gsim 1.5\times10^{-5}$ eV$^2$ and $4\times10^{-10}$ eV$^2\lsimΔm^2\lsim2\times10^{-7}$ eV$^2$ the full interval $|ε|<0.3$ is allowed within 4$σ$(99.995 % CL). We suggest ways to measure $ε$ in future experiments. The observable that is most sensitive to $ε$ is the rate [NC]/[CC] in combination with the Day-Night asymmetry in the SNO detector. With theoretical and statistical uncertainties, the expected accuracy after 5 years is $Δε\sim 0.07$. We also discuss the effects of maximal and near-maximal $ν_e$-mixing in atmospheric neutrinos, supernova neutrinos, and neutrinoless double beta decay.

hep-ph↗
arXiv2000

The minimum width condition for neutrino conversion in matter

We find that for small vacuum mixing angle $θ$ and low energies ($s\ll M^2_Z$) the width of matter, $d_{1/2}$, needed to have conversion probability $P\geq 1/2$ should be larger than $d_{min}= π/(2\sqrt{2} G_{F} \tan 2 θ)$: $d_{1/2}\geq d_{min}$. Here $G_F$ is the Fermi constant, $s$ is the total energy squared in the center of mass and $M_Z$ is the mass of the $Z$ boson. The absolute minimum $d_{1/2}=d_{min}$ is realized for oscillations in a uniform medium with resonance density. For all the other density distributions (monotonically varying density, castle wall profile, etc.) the required width $d_{1/2}$ is larger than $d_{min}$. The width $d_{min}$ depends on $s$, and for $Z$-resonance channels at $s\sim M^2_Z$ we get that $d_{min}(s)$ is 20 times smaller than the low energy value. We apply the minimum width condition, $d\geq d_{min}$, to high energy neutrinos in matter as well as in neutrino background. Using this condition, we conclude that the matter effect is negligible for neutrinos propagating in AGN and GRBs environments. Significant conversion can be expected for neutrinos crossing dark matter halos of clusters of galaxies and for neutrinos produced by cosmologically distant sources and propagating in the universe.

hep-ph↗
arXiv1999

Comment on "New conditions for a total neutrino conversion in a medium"

We show that the conditions for total neutrino conversion found in [1] are equivalent to the conditions of maximal depth (parametric resonance) and ($π/2 + πk$) - phase of parametric oscillations. Therefore the effects considered in [1] are a particular case of the parametric resonance in neutrino oscillations. The existence of strong enhancement peaks in transition probability P rather than the condition P=1 is of physical relevance. We comment on possible realizations and implications of the parametric enhancement of neutrino oscillations.

hep-ph↗
arXiv1999

Is Large Mixing Angle MSW the Solution of the Solar Neutrino Problems?

Recent results on solar neutrinos provide hints that the LMA MSW solution could be correct. We perform accurate calculations for potential `smoking-gun' effects of the LMA solution in the SuperKamiokande solar neutrino experiment, including: (1) an almost constant reduction of the standard recoil electron energy spectrum (with a weak, < 10%, relative increase below 6.5 MeV); (2) an integrated difference in day-night rates (2% to 14%); (3) an approximately constant zenith-angle dependence of the nighttime event rate; (4) a new test for the difference in the shape of the equally-normalized day-night energy spectra (~ 1%); and (5) annual variations of the signal due to the regeneration effect (~ 6 times smaller than the integrated day-night effect). We also establish a relation between the integrated day-night asymmetry and the seasonal asymmetry due to LMA regeneration. As a cautionary example, we simulate the effect of an absolute energy calibration error on the shape (distortion) of the recoil energy spectrum. We compare LMA predictions with SuperKamiokande data and discuss the possibilities for distinguishing experimentally between LMA and vacuum oscillations.

hep-ph↗
arXiv1999

Lepton Mixing: Small, Large, Maximal?

The SuperKamiokande data on atmospheric neutrinos imply that $ν_μ$ has large (or even maximal) mixing. It is still open question whether this mixing is the flavor one or mixing with singlet state (sterile neutrino). Several tests exist to establish the channel of atmospheric neutrino oscillations. Large mixing can be a property of the second and third generations, so that the scheme with single large mixing is realized. It can be a generic property of all leptons, thus leading to the bi-large or threefold large mixing schemes. The ambiguity will be resolved by identification of solution of the solar neutrino problem. In this review we consider phenomenology of various mixing schemes. The key measurements which will allow us to make significant step in reconstruction of the neutrino mass and flavor spectrum are discussed.

hep-ph↗
arXiv1999

Reconstructing Neutrino Mass Spectrum

Reconstruction of the neutrino mass spectrum and lepton mixing is one of the fundamental problems of particle physics. In this connection we consider two central topics: (i) the origin of large lepton mixing, (ii) possible existence of new (sterile) neutrino states. We discuss also possible relation between large mixing and existence of sterile neutrinos.

hep-ph↗
arXiv1998

Neutrino Conversion and Neutrino Astrophysics

We consider main ingredients which determine neutrino transformations in media. Strong transformations relevant for the astrophysics can be due to large depth oscillations, resonance conversion, parametric resonance effect, interplay of oscillations and inelastic collisions. Properties of transitions are discussed using the graphic representation. The applications of the transitions to supernova neutrinos are described. The supernova neutrinos can probe whole neutrino mass spectrum. Their studies will help to identify the pattern of neutrino mass and mixing.

hep-ph↗
arXiv1998

Atmospheric neutrinos at Super-Kamiokande and parametric resonance in neutrino oscillations

We consider the oscillations of atmospheric neutrinos in the earth in the three-neutrino scheme with a $Δm^2$ hierarchy and a small admixture of the electron neutrino in the heavy mass eigenstate characterized by the mixing angle $θ_{13}$. We show that for $Δm^2 \simeq (0.5 - 3) \times 10^{-3}$ eV$^2$ indicated by the Super-Kamiokande data and $\sin^2 2θ_{13} \aprle 0.2$, the oscillations of multi-GeV neutrinos in the subdominant $ν_μ \leftrightarrow ν_e$ mode are enhanced by the MSW and parametric resonances. The parametric resonance, which occurs when the neutrinos cross the core of the earth, dominates for $Δm^2 \simeq (1 - 2)\times 10^{-3}$ eV$^2$, $\sin^2 2θ_{13} \aprle 0.06$. The resonance matter effects lead to an observable excess of the e-like events with a specific zenith angle dependence even for small $θ_{13}$. The up-down asymmetry of the multi-GeV e-like events can reach 15% for $|\cos Θ_e| > 0.2$ and up to 30% for $|\cos Θ_e| > 0.6$, where $Θ_e$ is the zenith angle of the electron. The resonance matter effects are relevant for the interpretation of the Super-Kamiokande data.

hep-ph↗
arXiv1998

Towards the Solution of the Solar Neutrino Problem

We discuss various aspects of the solar neutrino spectrum distortion and time variations of fluxes. (i) Oscillations of neutrinos which cross the mantle and the core of the Earth can be parametrically enhanced. The parametric effect gives correct physical interpretation of the calculated day-night asymmetry. (ii) Solution of the $ν_{\odot}$-problem in schemes with three and more neutrinos which accommodate explanations of other neutrino anomalies, in particular, the atmospheric neutrino anomaly, can lead to complicated distortion of the boron neutrino spectrum. (iii) The study of correlations between time (seasonal or day-night) variations and spectrum distortion will help to identify the solution of the $ν_{\odot}$-problem.

hep-ph↗
arXiv1998

Where do we stand with solar neutrino oscillations?

We determine the neutrino parameters for MSW and vacuum oscillations (active and sterile neutrinos) that are allowed by the separate, and collective, imposition of the constraints from total event rates in the chlorine, GALLEX, SAGE, and SuperKamiokande experiments (504 days), the SuperKamiokande electron energy spectrum, and the SuperKamiokande zenith-angle dependence. The small mixing angle MSW solution is acceptable at the 7% C.L. (8% for sterile nu's) and the vacuum solution is acceptable at the 6% C.L. . The best-fit global MSW solution for active neutrinos is: Delta m^2 = 5 x 10^-6 eV^2, sin^2 (2 theta) = 5.5 x 10^{-3} (and for sterile neutrinos: Delta m^2 = 4 x 10^-6 eV^2, sin^2 (2 theta) = 7 x 10^-3). For vacuum oscillations, the best-fit solution is: Delta m^2 = 6.5 x 10^-11 eV^2, sin^2 (2 theta) = 0.75 . An arbitrary combination of undistorted (no oscillations) pp, 7Be, 8B, and CNO neutrino fluxes is inconsistent with the combined data sets at the 3.5 sigma C.L., independent of astrophysical considerations. We use improved calculations of solar model fluxes, neutrino absorption cross sections and energy spectra, and a detailed evaluation of regeneration effects.

hep-ph↗
arXiv1998

Baryogenesis via neutrino oscillations

We propose a new mechanism of leptogenesis in which the asymmetries in lepton numbers are produced through the CP-violating oscillations of ``sterile'' (electroweak singlet) neutrinos. The asymmetry is communicated from singlet neutrinos to ordinary leptons through their Yukawa couplings. The lepton asymmetry is then reprocessed into baryon asymmetry by electroweak sphalerons. We show that the observed value of baryon asymmetry can be generated in this way, and the masses of ordinary neutrinos induced by the seesaw mechanism are in the astrophysically and cosmologically interesting range. Except for singlet neutrinos, no physics beyond the Standard Model is required.

hep-ph↗
arXiv1998

Rescuing Grand Unification Scenario for Neutrino Mass

The see-saw mechanism for neutrino masses based on the Grand Unification leads to the mass of the heaviest neutrino ($\approx ν_τ$) in the range $(2 - 3)\cdot 10^{-3}$ eV and hence to a solution of the solar neutrino problem through the $ν_e-ν_\t$ conversion. We suggest the existence of a light singlet fermion $S$ which mixes predominantly with muon neutrino through the mixing mass $m_{μs} \sim O(1)$ eV. The introduction of such a singlet allows one (i) to solve the atmospheric neutrino problem via the $ν_μ \leftrightarrow S$ oscillations, (ii) to explain the LSND result and (iii) to get two component hot dark matter in the Universe. The phenomenology of this scenario is considered and the origin of the singlet as well as of the scale $m_{\m s}$ is discussed.

hep-ph↗
arXiv1998

Neutrino Mass Spectrum with $ν_μ$ $\to$ $ν_s$ Oscillations of Atmospheric Neutrinos

We consider the ``standard'' spectrum of the active neutrinos (characterized by strong mass hierarchy and small mixing) with additional sterile neutrino, $ν_s$. The sterile neutrino mixes strongly with the muon neutrino, so that $ν_μ \leftrightarrow ν_s$ oscillations solve the atmospheric neutrino problem. We show that the parametric enhancement of the $ν_μ \leftrightarrow ν_s$ oscillations occurs for the high energy atmospheric neutrinos which cross the core of the Earth. This can be relevant for the anomaly observed by the MACRO experiment. Solar neutrinos are converted both to $ν_μ$ and $ν_s$. The heaviest neutrino ($\approx ν_τ$) may compose the hot dark matter of the Universe. Phenomenology of this scenario is elaborated and crucial experimental signatures are identified. We also discuss properties of the underlying neutrino mass matrix.

hep-ph↗
arXiv1998

Parametric Resonance in Oscillations of Atmospheric Neutrinos?

We consider a solution of the atmospheric neutrino problem based on oscillations of muon neutrinos to sterile neutrinos: $ν_μ$ $\leftrightarrow$ $ν_s$. The zenith angle ($Θ$) dependences of the neutrino and upward-going muon fluxes in presence of these oscillations are studied. The dependences have characteristic form with two dips: at $\cos Θ= -0.6 ÷-0.2$ and $\cos Θ= -1.0 ÷-0.8$. The latter dip is due to parametric resonance in oscillations of neutrinos which cross the core of the earth. A comparison of predictions with data from the MACRO, Baksan and Super-Kamiokande experiments is given.

hep-ph↗
arXiv1997

Solar neutrinos and grand unification

We consider the Grand Unification (GU) scenario for neutrino masses which is based on the see-saw mechanism with the mass of the heaviest right handed (RH) neutrino at the GU-scale: $M_3 \sim Λ_{GU}$, and on the quark-lepton symmetry for fermions from the third generation. The scenario predicts for the light neutrinos: $m_3 \sim (2 - 4) \cdot 10^{-3}$ eV and $m_2 \sim (0.3 - 3) \cdot 10^{-5}$ eV (in the case of a linear mass hierarchy of the RH neutrinos or/and in presence of the Planck scale suppressed non-renormalizable operators). It also predicts large $ν_e - ν_μ$ mixing: $~\sin^2 2θ_{eμ} \stackrel{_>}{_\sim} 0.2$. In this scenario the solar neutrinos ($ν_{\odot}$) undergo both the \nue $\to$ \nutau resonance conversion in the Sun and substantial \nue $\to$ \numu vacuum oscillations on the way from the Sun to the Earth. The interplay of both effects enlarges the range of neutrino parameters which solve the $ν_{\odot}$-problem. In particular, $ν_e - ν_τ$ mixing angle can be as small as the corresponding quark mixing: $\sin^2 2θ_{eτ} \geq (2~-~5) \cdot 10^{-4}$. The scenario predicts peculiar (oscillatory) distortion of the boron neutrino energy spectrum and seasonal variations of signals. Manifestations of these effects in the Super-Kamiokande and SNO experiments are studied.

hep-ph↗
arXiv1997

Vacuum oscillations of solar neutrinos: correlation between spectrum distortion and seasonal variations

Long length vacuum oscillations solution of the solar neutrino problem is discussed. We show that there is a strict correlation between a distortion of the neutrino energy spectrum and an amplitude of seasonal variations of the neutrino flux. The slope parameter which characterizes a distortion of the recoil electron energy spectrum in the Super-Kamiokande experiment and the seasonal asymmetry of the signal have been calculated in a wide range of oscillation parameters. The correlation of the slope and asymmetry gives crucial criteria for identification or exclusion of this solution. For the positive slope indicated by preliminary Super-Kamiokande data we predict (40 - 60) % enhancement of the seasonal variations.

hep-ph↗
arXiv1997

Neutrino Conversions in a Polarized Medium

Electron polarization induced by magnetic fields can modify the potentials relevant for describing neutrino conversions in media with magnetic fields. The magnitudes of polarization potentials are determined for different conditions. We show that variations of the electron polarization along the neutrino trajectory can induce resonant conversions in the active-sterile neutrino system, but cannot lead to level crossing in the active-active neutrino system. For neutrino flavour conversions the polarisation leads only to a shift of the standard MSW resonance. For polarizations $λ\lsim 0.04$ the direct modifications of the potential (density) due to the magnetic field pressure are smaller than the modifications due to the polarization effect. We estimate that indeed the typical magnitude of the polarization in the sun or in a supernova are not expected to exceed $10^{-2}$. However even such a small polarization may lead to interesting consequences for supernova physics and for properties of neutrino signals from collapsing stars.

hep-ph↗