arXiv subjects

Alexei Yu. Smirnov

Publications and source records attributed to Alexei Yu. Smirnov.

68 records · Page 4Linked to original sources

arXiv1998

Neutral-to-charged current events ratio in atmospheric neutrinos and neutrino oscillations

The atmospheric neutrinos produce isolated neutral pions ($π^0$-events) mainly in the neutral current interactions. We propose to study the ratios involving $π^0$-events and the events induced mainly by the charged currents. This minimizes uncertainties related to the original neutrino fluxes, and in certain cases, also to the cross-sections. Experimental study of these ratios will allow one to check the oscillation solution of the atmospheric neutrino problem and to identify the channel of oscillations. Illustrative analysis of existing data is presented.

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arXiv1997

Neutrino - Modulino Mixing

We suggest the existence of a light singlet fermion, $S$, which interacts with observable matter only via a Planck mass suppressed interaction: $\sim m_{3/2}/M_P$, where $m_{3/2}$ is the supergravity gravitino mass. If the mass of the singlet equals $\sim m_{3/2}^2/M_P$, then $ν_e \to S$ resonance conversion solves the solar neutrino problem or leads to observable effects. The $νS$-mixing changes supernova neutrino fluxes and has an impact on the primordial nucleosynthesis. The singlet $S$ can originate as the supersymmetric partner of the moduli fields in supergravity or low energy effective theory steaming from superstrings. The $νS$-mixing may be accompanied by observable R-parity breaking effects.

hep-ph↗

arXiv1996

Neutrino Masses and Oscillations

New effects related to refraction of neutrinos in different media are reviewed and implication of the effects to neutrino mass and mixing are discussed. Patterns of neutrino masses and mixing implied by existing hints/bounds are described. Recent results on neutrino mass generation are presented. They include neutrino masses in SO(10) GUT's and models with anomalous $U(1)$, generation of neutrino mass via neutrino-neutralino mixing, models of sterile neutrino.

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arXiv1996

Long range neutrino forces and the lower bound on neutrino mass

Stellar objects (including our Sun, other stars of main sequence, white dwarfs, neutron stars etc.) contain strongly degenerate low energy sea of neutrinos (in neutron stars) or antineutrinos. The presence of this sea leads due to Pauli principle and thermal effects to effective blocking of the long-range neutrino forces. This blocking can resolve the problem of the unphysically large value of the self-energy of stars stipulated by many body long-range neutrino interactions. As a consequence no lower bound on the neutrino mass is inferred, in contrast with the statement by Fischbach.

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arXiv1996

High Energy Cosmic Neutrinos and the Equivalence Principle

Observation of the ultra-high energy neutrinos, in particular, detection of $ν_τ$ from cosmologically distant sources like active galactic nuclei (AGN) opens new possibilities to search for neutrino flavor conversion. We consider effects of violation of the equivalence principle (VEP) on propagation of these cosmic neutrinos. Two effects are studied: (1) the oscillations of neutrinos due to the VEP in the gravitational field of our Galaxy and in the intergalactic space, (2) the resonance flavor conversion driven by the gravitational potential of the AGN. We show that the ultra-high energies of the neutrinos as well as cosmological distances to the AGN, or strong AGN gravitational potential will allow one to improve the accuracy of test of the equivalence principle by 21 orders of magnitude for massless or degenerate neutrinos ($Δf \sim 10^{-41}$) and at least by 12 orders of magnitude for massive neutrinos ($Δf \sim 10^{-28} \times (Δm^2/1 {\rm eV}^2)$). Experimental signatures of the transitions induced by the VEP are discussed.

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arXiv1996

Is Zee Model The Model of Neutrino Masses?

Zee model leads naturally to two heavy, strongly degenerate and almost maximally mixed neutrinos and to one light neutrino with small mixing. This pattern coincides with the one needed for a solution of the atmospheric neutrino problem by $\n_\m\A \n_τ$ oscillations and for existence of the two component hot dark matter in the Universe. Furthermore, the oscillations $\bar\n_\m\A \bar\n_e$ can be in the range of sensitivity of KARMEN, LSND experiments. Phenomenology of this scenario is considered and possibility to check it in the forthcoming experiments is discussed. Scenario implies large values and inverse flavour hierarchy of the couplings of the Zee boson with fermions: $f_{e τ} \ll f_{μτ} \leq f_{e μ} \sim 0.1$. Main signatures of scenario are: strongly suppressed signal of $\n_\m\A \n_τ$ oscillation in CHORUS and NOMAD experiments, so that positive result from these experiments will rule out the scenario; possibility of observation of $\n_e\A \n_τ$ oscillations by CHORUS and NOMAD; corrections to the muon decay, neutrino-electron scattering at the level of the experimental errors; branching ratio $B(μ\A e γ)$ bigger than $10^{-13}$. The solar neutrino problem can be solved by introduction of additional very light singlet fermion without appreciable changes of the active neutrino pattern.

hep-ph↗

arXiv1996

Large $R$-parity Violating Couplings and Grand Unification

We consider a possibility that $R$-parity violating interactions of particles which do not involve the first generation have large (up to 1) coupling constants, $Λ$. Such couplings, if exist, could have a number of phenomenological consequences: renormalization of $b-τ$ mass ratio, generation of $ν_τ$ mass in MeV region, {\em etc.}. In Grand Unified models, where $B$- and $L$-violating couplings appear simultaneously, the proton decay can be forbidden in virtue of hierarchical flavor structure of $Λ.$ However, due to Cabibbo-Kobayashi-Maskawa mixing this decay is induced already in one-loop. Present experimental data give the upper bound $Λ\ltap 10^{-8}$ (or $|λ' λ''| \ltap 7\cdot 10^{-16},$ on products of certain $L$- and $B$-violating coupling constants, in more general context). The bound can be avoided, if there is an asymmetry between the $L$- and $B$-violating couplings of usual matter fields. In the $SU(5)$ model the asymmetry can be related to the doublet-triplet splitting.

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arXiv1996

Upper bound on all products of R-parity violating couplings $λ'$ and $λ''$ from proton decay

We prove that {\em any} product of R-parity violating couplings $λ'$ (L-violating) and $λ''$ (B-violating) can be strongly restricted by proton decay data. For any pair $λ'$ and $λ''$ the decay exists at least at one loop level. For squark masses below 1 TeV we find the conservative bounds $|λ' \cdot λ''| < 10^{-9}$ in absence of squark flavor mixing, and $|λ' \cdot λ''| < 10^{-11}$ when this mixing is taken into account. We study the dependence of the bounds on the flavor basis in which R-parity breaking couplings are determined.

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arXiv1994

The Solar Neutrino Problem: Neither Astrophysics Nor Oscillations?

There is no consistent solar model which can describe all experimental data on the solar neutrinos. The problem can be formulated essentially in a model independent way. The key points are the comparison of the Homestake and the Kamiokande data as well as the comparison of the GALLEX and SAGE results with minimal signal estimated from the solar luminosity. It is argued than in such a comparison one should use the Homestake-II data (only after 1986) with caution. The results of the model independent analysis show strong suppression of the beryllium neutrino flux. The data can be well described by the resonant flavor conversion. For the ``low flux model" which can accommodate the Kamiokande signal, a consistent solution can be found for the neutrino mass squared difference $Δm^2 = (0.3 - 1.0)\cdot 10^{-5}$ eV$^2$ and values of mixing angle $\sin^2 2θ> 5 \cdot 10^{-4}$ (``very small mixing solution").

hep-ph↗

arXiv1994

Neutrinos with Zee-Mass Matrix in Vacuum and Matter

Neutrino mass matrix generated by the Zee (radiative) mechanism has zero (in general, small) diagonal elements and a natural hierarchy of the nondiagonal elements. It can be considered as an alternative (with strong predictive power) to the matrices generated by the see-saw mechanism. The propagation in medium of the neutrinos with the Zee-mass matrix is studied. The flavor neutrino transitions are described analytically. In the physically interesting cases the probabilities of transitions as functions of neutrino energy can be represented as two-neutrino probabilities modulated by the effect of vacuum oscillations related to the small mass splitting. Possible applications of the results to the solar, supernova, atmospheric and relic neutrinos are discussed. A set of the predictions is found which could allow to identify the Zee-mass matrix and therefore the corresponding mechanism of mass generation.

hep-ph↗

arXiv1993

Results from Neutrino Experiments

Recent (first or/and the best) results from the neutrino experiments are reviewed and their implications for the theory are discussed. The sense of the experiments is the searching for neutrino masses, mixing and interactions beyond the standard model. Present laboratory experiments give upper bounds on the masses and the mixing which are at the level of predictions of the ``electroweak see-saw". Positive indications of nonzero lepton mixing follow from studies of the solar and atmospheric neutrinos.

hep-ph↗

arXiv1993

Neutrino Masses and Mixing

Restrictions on the neutrino masses and lepton mixing are reviewed. Solar, atmospheric and relic neutrinos give the indications of existence of nonzero neutrino masses and mixing. The data pick up two regions of mixing angles which are or appreciably larger or appreciably smaller than the Cabibbo angle. Some theoretical schemes with {\it large} or {\it small} lepton mixing are discussed.

hep-ph↗

arXiv1993

Is Large Lepton Mixing Excluded?

The original \bnum -(or $\barν_τ$-) energy spectrum from the gravitational collapse of a star has a larger average energy than the spectrum for \bnue since the opacity of \bnue exeeds that of \bnum (or $ν_τ$). Flavor neutrino conversion, \bnue $\leftrightarrow$ \bnum, induced by lepton mixing results in partial permutation of the original \bnue and \bnum spectra. An upper bound on the permutation factor, $p \leq 0.35$ (99$\%$ CL) is derived using the data from SN1987A and the different models of the neutrino burst. The relation between the permutation factor and the vacuum mixing angle is established, which leads to the upper bound on this angle. The excluded region, $\sin^2 2θ> 0.7 - 0.9$, covers the regions of large mixing angle solutions of the solar neutrino problem: ``just-so" and, partly, MSW, as well as part of region of $ν_{e} - ν_μ$ oscillation space which could be responsible for the atmospheric muon neutrino deficit. These limits are sensitive to the predicted neutrino spectrum and can be strengthened as supernova models improve.

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arXiv1993

See-saw Enhancement of Lepton Mixing

The see-saw mechanism of neutrino mass generation may enhance lepton mixing up to maximal even if the Dirac mass matrices of leptons have structure similar to that in the quark sector. Two sets of conditions for such an enhancement are found. The first one includes the see-saw generation of heavy Majorana masses for right-handed neutrinos and a universality of Yukawa couplings which can follow from the unification of neutrinos with new superheavy neutral leptons. The second set is related to lepton number symmetry of the Yukawa interactions in the Dirac basis of neutrinos. Models which realize these conditions have strong hierarchy or strong degeneration of Majorana masses of the right-handed neutrinos.

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