arXiv subjects

Alexei Yu. Smirnov

Publications and source records attributed to Alexei Yu. Smirnov.

At least 55 records · Page 3Linked to original sources

arXiv2006

Quark lepton complementarity and renormalization group effects

We consider a scenario for the Quark-Lepton Complementarity relations between mixing angles in which the bi-maximal mixing follows from the neutrino mass matrix. According to this scenario in the lowest order the angle θ_{12} is \sim 1σ(1.5 - 2^\circ) above the best fit point coinciding practically with the tri-bimaximal mixing prediction. Realization of this scenario in the context of the seesaw type-I mechanism with leptonic Dirac mass matrices approximately equal to the quark mass matrices is studied. We calculate the renormalization group corrections to θ_{12} as well as to θ_{13} in the standard model (SM) and minimal supersymmetric standard model (MSSM). We find that in large part of the parameter space corrections Δθ_{12} are small or negligible. In the MSSM version of the scenario the correction Δθ_{12} is in general positive. Small negative corrections appear in the case of an inverted mass hierarchy and opposite CP parities of ν_1 and ν_2 when leading contributions to θ_{12} running are strongly suppressed. The corrections are negative in the SM version in a large part of the parameter space for values of the relative CP phase of ν_1 and ν_2: ϕ> π/2.

hep-ph↗

arXiv2006

Sterile neutrinos: direct mixing effects versus induced mass matrix of active neutrinos

Mixing of active neutrinos with sterile ones generate ``induced'' contributions to the mass matrix of active neutrinos $\sim m_S \sin^2θ_{aS}$, where $m_S$ is the Majorana mass of the sterile neutrino and $θ_{aS}$ is the active-sterile mixing angle. We study possible effects of the induced matrix which can modify substantially the implications of neutrino oscillation results. We have identified the regions of $m_S$ and $\sin^2θ_{aS}$ where the induced matrix (i) provides the dominant structures, (ii) gives the sub-dominant effects and (iii) where its effects can be neglected. The induced matrix can be responsible for peculiar properties of the lepton mixing and neutrino mass spectrum, in particular, it can generate the tri-bimaximal mixing. We update and discuss bounds on the induced masses from laboratory measurements, astrophysics and cosmology. We find that substantial impact of the induced matrix is possible if $m_S \sim 0.1-1$ eV and $\sin^2θ_{aS} \sim 10^{-3} - 10^{-2}$ or $m_S \geq 200$ MeV and $\sin^2θ_{aS} \leq 10^{-9}$. The bounds can be relaxed in cosmological scenarios with low reheating temperature, if sterile neutrinos decay sufficiently fast, or their masses change with time.

hep-ph↗

arXiv2005

Neutrino masses and mixing

Status of determination of the neutrino masses and mixing is formulated and possible uncertainties, especially due to presence of the sterile neutrinos, are discussed. The data hint an existence of special ``neutrino'' symmetries. If not accidental these symmetries have profound implications and can substantially change the unification program. The key issue on the way to underlying physics is relations between quarks and leptons. The approximate quark-lepton symmetry or universality can be reconciled with strongly different patterns of masses and mixings due to nearly singular character of the mass matrices or screening of the Dirac structures in the double see-saw mechanism.

hep-ph↗

arXiv2005

Solar neutrinos and 1-3 leptonic mixing

Effects of the 1-3 leptonic mixing on the solar neutrino observables are studied and the signatures of non-zero $θ_{13}$ are identified. For this we have re-derived the formula for $3ν$-survival probability including all relevant corrections and constructed the iso-contours of observables in the $\sin^2 θ_{12} - \sin^2 θ_{13}$ plane. Analysis of the solar neutrino data gives $\sin^2θ_{13} = 0.007^{+ 0.080}_{-0.007}$ (90% C.L.) for $Δm^2 = 8 \cdot 10^{-5}$ eV$^2$. The combination of the ratio CC/NC at SNO and gallium production rate selects $\sin^2θ_{13} = 0.017 \pm 0.026$ ($1σ$). The global fit of all oscillation data leads to zero best value of $\sin^2 θ_{13}$. The sensitivity ($1σ$ error) of future solar neutrino studies to $\sin^2 θ_{13}$ can be improved down to 0.01 - 0.02 by precise measurements of the pp-neutrino flux and the CC/NC ratio as well as spectrum distortion at high ($E > 4$ MeV) energies. Combination of experimental results sensitive to the low and high energy parts of the solar neutrino spectrum resolves the degeneracy of angles $θ_{13}$ and $θ_{12}$. Comparison of $\sin^2 θ_{13}$ as well as $\sin^2 θ_{12}$ measured in the solar neutrinos and in the reactor/accelerator experiments may reveal new effects which can not be seen otherwise.

hep-ph↗

arXiv2005

Screening of Dirac flavor structure in the seesaw and neutrino mixing

We consider the mechanism of screening of the Dirac flavor structure in the context of the double seesaw mechanism. As a consequence of screening, the structure of the light neutrino mass matrix, m_ν, is determined essentially by the structure of the (Majorana) mass matrix, M_S, of new super-heavy (Planck scale) neutral fermions S. We calculate effects of the renormalization group running in order to investigate the stability of the screening mechanism with respect to radiative corrections. We find that screening is stable in the supersymmetric case, whereas in the standard model it is unstable for certain structures of M_S. The screening mechanism allows us to reconcile the (approximate) quark-lepton symmetry and the strong difference of the mixing patterns in the quark and lepton sectors. It opens new possibilities to explain a quasi-degenerate neutrino mass spectrum, special ``neutrino'' symmetries and quark-lepton complementarity. Screening can emerge from certain flavor symmetries or Grand Unification.

hep-ph↗

arXiv2004

Alternatives to the seesaw mechanism

The observed pattern of lepton mixing does not give an evidence of the seesaw. It is easier to disprove seesaw showing that one of the alternatives gives dominant contribution to the neutrino mass. We consider alternative mechanisms based on (i) small (tree level) effective couplings, (ii) small VEV, (iii) radiative generation of masses, (iv) protection by SUSY breaking scale or by $μ$-term, (v) small overlap of wave functions of the left and right handed neutrino components in extra dimensions. Seesaw can be the mechanism of suppression of the Dirac mass terms and not dominant mechanism of the neutrino mass giving just a sub-leading contribution.

hep-ph↗

arXiv2004

Neutrino Mixing and Quark-Lepton Complementarity

As a result of identification of the solution to the solar neutrino problem, a rather precise relation theta_{sun} + theta_C = pi/4 between the leptonic 1-2 mixing angle theta_{sun} and the Cabibbo angle has emerged. It would mean that the lepton and the quark mixing angles add up to the maximal, suggesting a deep structure by which quarks and leptons are interrelated. We refer the relation ``quark-lepton complementarity'' (QLC) in this paper. We formulate general conditions under which the QLC relation is realized. We then present several scenarios which lead to the relation and elaborate on phenomenological consequences which can be tested by the future experiments. We also discuss implications of the QLC relation for the quark-lepton symmetry and the mechanism of neutrino mass generation.

hep-ph↗

arXiv2003

Probing the seesaw mechanism with neutrino data and leptogenesis

In the framework of the seesaw mechanism with three heavy right-handed Majorana neutrinos and no Higgs triplets we carry out a systematic study of the structure of the right-handed neutrino sector. Using the current low-energy neutrino data as an input and assuming hierarchical Dirac-type neutrino masses $m_{Di}$, we calculate the masses $M_i$ and the mixing of the heavy neutrinos. We confront the inferred properties of these neutrinos with the constraints coming from the requirement of a successful baryogenesis via leptogenesis. In the generic case the masses of the right-handed neutrinos are highly hierarchical: $M_i \propto m_{Di}^2$; the lightest mass is $M_1 \approx 10^3 - 10^6$ GeV and the generated baryon-to-photon ratio $η_B\lesssim 10^{-14}$ is much smaller than the observed value. We find the special cases which correspond to the level crossing points, with maximal mixing between two quasi-degenerate right-handed neutrinos. Two level crossing conditions are obtained: ${m}_{ee}\approx 0$ (1-2 crossing) and $d_{12}\approx 0$ (2-3 crossing), where ${m}_{ee}$ and $d_{12}$ are respectively the 11-entry and the 12-subdeterminant of the light neutrino mass matrix in the basis where the neutrino Yukawa couplings are diagonal. We show that sufficient lepton asymmetry can be produced only in the 1-2 crossing where $M_1 \approx M_2 \approx 10^{8}$ GeV, $M_3 \approx 10^{14}$ GeV and $(M_2 - M_1)/ M_2 \lesssim 10^{-5}$.

hep-ph↗

arXiv2003

Neutrino Physics after KamLAND

The neutrino anomalies were driving force of the developments in neutrino physics during the last 30 - 35 years. I will consider status of the anomalies after the first KamLAND result. The main questions are "What is left?" and "What is the next?" In the new phase, the phenomenological objectives of neutrino physics consist of accomplishing the program of reconstruction of the neutrino mass and flavor spectrum and searches for physics beyond the ``standard'' picture. The latter includes searches for new (sterile) neutrino states, new neutrino interactions, effects of violation of the fundamental symmetries in the neutrino sector.

hep-ph↗

arXiv2003

Matter Effects of Thin Layers: Detecting Oil by Oscillations of Solar Neutrinos

We consider a possibility to use the solar neutrinos for studies of small scale structures of the Earth and for geological research. Effects of thin layers of matter with density contrast on oscillations of Beryllium neutrinos inside the Earth are studied. We find that change of the $^7Be$ neutrino flux can reach 0.1 % for layers with density of oil and size 20 km. Problems of detection are discussed. Hypothetical method would consist of measuring the $^7Be -$ flux by, {\it e.g.}, large deep underwater detector$-$submarine which could change its location.

hep-ph↗

arXiv2003

Radiative corrections to neutrino mass matrix in the Standard Model and beyond

We study the effect of radiative corrections on the structure of neutrino mass matrix. We analyze the renormalization of the matrix from the electroweak scale $m_Z$ to the scale $m_0$ at which the effective operator that gives masses to neutrinos is generated. Apart from Standard Model and MSSM, non-standard extensions of SM are considered at a scale $m_X$ intermediate between $m_Z$ and $m_0$. We find that the dominant structure of the neutrino mass matrix does not change. SM and MSSM corrections produce small (few percents) independent renormalization of each matrix element. Non-standard (flavor changing) corrections can modify strongly small (sub-dominant) matrix elements, which are important for the low energy phenomenology. In particular, we show that all sub-dominant elements can have purely radiative origin, being zero at $m_0$. The set of non-zero elements at $m_0$ can be formed by (i) diagonal elements (unit matrix); (ii) $M_{ee}$ and $M_{μτ}$; (iii)$M_{ee}$ and $μτ$-block elements; (iv) $μτ$-block elements. In the case of unit matrix, both atmospheric and solar mixing angles and mass squared differences are generated radiatively.

hep-ph↗

arXiv2002

Structure of neutrino mass matrix and CP violation

We reconstruct the neutrino mass matrix in the flavor basis, using all available experimental data on neutrino oscillations. Majorana nature of neutrinos, normal mass hierarchy (ordering) and validity of the LMA MSW solution of the solar neutrino problem are assumed. We study dependences of the mass matrix elements, m_{alpha beta}, on the CP violating Dirac, delta, and Majorana, rho, sigma, phases, for different values of the mixing angle theta_{13} and of the absolute mass scale, m_1. The contours of constant mass in the rho-sigma plane have been constructed for all m_{alpha beta}. These rho-sigma plots allow to systematically scan all possible structures of the mass matrix. We identify regions of parameters in which the matrix has (i) a structure with the dominant mu tau-block, (ii) various hierarchical structures, (iii) flavor alignment, (iv) structures with special ordering or equalities of elements, (v) the democratic form. In certain cases the matrix can be parameterized by powers of a unique expansion (ordering) parameter lambda approximately 0.2 - 0.3 (lambda_{ord} approximately 0.6 - 0.7). Perspectives to further restrict the structure of mass matrix in future experiments, in particular in the beta beta_{0 nu}-decay searches, are discussed.

hep-ph↗

arXiv2001

Solar neutrinos: global analysis and implications for SNO

We present a global analysis of all the available solar neutrino data treating consistently the 8B and hep neutrino fluxes as free parameters. The analysis reveals at 99.7% C.L. eight currently-allowed discrete regions in two-neutrino oscillation space, five regions corresponding to active neutrinos and three corresponding to sterile neutrinos. Most of the allowed solutions are robust with respect to changes in the analysis procedure, but the traditional vacuum solution is fragile. The globally-permitted range of the 8B neutrino flux, 0.45 to 1.95 in units of the BP2000 flux, is comparable to the 3 sigma range allowed by the standard solar model. We discuss the implications for SNO of a low mass, Delta m^2 ~ 6 times 10^{-12} eV^2, vacuum oscillation solution, previously found by Raghavan, and by Krastev and Petcov, but absent in recent analyses that included Super-Kamiokande data. For the SNO experiment, we present refined predictions for the charged-current rate and the ratio of the neutral-current rate to charged-current rate. The predicted charged-current rate can be clearly distinguished from the no-oscillation rate only for the LMA solution. The predicted ratio of the neutral-current rate to charged-current rate is distinguishable from the no-oscillation ratio for the LMA, SMA, LOW, and VAC solutions for active neutrinos.

hep-ph↗

arXiv2000

Correlations of Solar Neutrino Observables for SNO

Neutrino oscillation scenarios predict correlations, and zones of avoidance, among measurable quantities such as spectral energy distortions, total fluxes, time dependences, and flavor content. The comparison of observed and predicted correlations will enhance the diagnostic power of solar neutrino experiments. A general test of all presently-allowed (two neutrino) oscillation solutions is that future measurements must yield values outside the predicted zones of avoidance. To illustrate the discriminatory power of the simultaneous analysis of multiple observables, we map currently allowed regions of neutrino masses and mixing angles onto planes of quantities measurable with the Sudbury Neutrino Observatory (SNO). We calculate the correlations that are predicted by vacuum and MSW (active and sterile) neutrino oscillation solutions that are globally consistent with all available neutrino data. We derive approximate analytic expressions for the dependence of individual observables and specific correlations upon neutrino oscillations parameters. We also discuss the prospects for identifying the correct oscillation solution using multiple SNO observables.

hep-ph↗

arXiv2000

SNO: Predictions for Ten Measurable Quantities

We calculate the range of predicted values for 10 quantities that will be measured by the Sudbury Neutrino Observatory (SNO). We use neutrino oscillation solutions (vacuum and MSW; active and sterile neutrinos) that are globally consistent with all available neutrino data and estimate realistic theoretical and experimental uncertainties. The neutral current to charged current double ratio is predicted to be more than 9 sigma from the no-oscillation solution for all of the currently favored neutrino oscillation solutions. The best-fit oscillation solutions predict a CC day-night rate difference between -0.1% and +12.5% and a NC day-night difference < 0.01%. We present also the predicted range for the first and the second moments of the charged current electron recoil energy spectrum, the charged current, the neutral current, and the neutrino-electron scattering rates, the seasonal dependence of the charged current rate, and the double ratio of neutrino-electron scattering rate to charged current rate.

hep-ph↗

arXiv1999

Identifying the neutrino mass spectrum from a supernova neutrino burst

We study the role that the future detection of the neutrino burst from a galactic supernova can play in the reconstruction of the neutrino mass spectrum. We consider all possible 3$ν$ mass and flavor spectra which describe the solar and atmospheric neutrino data. For each of these spectra we find the observable effects of the supernova neutrino conversions both in the matter of the star and the earth. We show that studies of the electron neutrino and anineutrino spectra as well as observations of the neutral current effects from supernova will allow us (i) to identify the solar neutrino solution, (ii) to determine the type of mass hierarchy (normal or inverted) and (iii) to probe the mixing $|U_{e3}|^2$ to values as low as $10^{-4} - 10^{-3}$.

hep-ph↗

arXiv1999

Probing Large Extra Dimensions with Neutrinos

We study implications of theories with sub-millimeter extra dimensions and $M_f \sim (1 - 10) $ TeV scale quantum gravity for neutrino physics. In these theories, the left-handed neutrinos as well as other standard model (SM) particles, are localized on a brane embedded in the bulk of large extra space. Mixing of neutrinos with (SM) singlet fermions propagating in the bulk is naturally suppressed by the volume factor $M_f/M_P \sim 3\cdot 10^{-16} - 3\cdot 10^{-15}$, where $M_P$ is the Planck mass. Properties of the neutrino oscillations and the resonance conversion to the bulk fermions are considered. We show that the resonance conversion of the electron neutrinos to the light bulk fermions can solve the solar neutrino problem. The signature of the solution is the peculiar distortion of the solar neutrino spectrum. The solution implies that the radius of at least one extra dimension should be in the range 0.06 - 0.1 mm {\it irrespective} of total number of extra dimensions. The corresponding modification of the Newtonian law is within the range of sensitivity of proposed sub-millimeter experiments, thus providing a verifiable link between neutrino physics and the gravity measurements.

hep-ph↗

arXiv1999

Coherence and the Day - Night Asymmetry in the Solar Neutrino Flux

We consider the day-night asymmetries predicted by MSW solutions of the solar neutrino problem. The integration over the neutrino energy, as well as over the production region or over the time intervals of more than a day leads to the averaging of oscillations on the way to the earth. This is equivalent to considering the neutrino state arriving at the surface of the earth as an incoherent mixture of the neutrino mass eigenstates (even if there is no divergence of wavepackets). As a consequence, the $ν_e$-regeneration effect inside the earth is incoherent, in contrast with the result in hep-ph/9902435.

hep-ph↗