arXiv subjects

E. Kh. Akhmedov

Publications and source records attributed to E. Kh. Akhmedov.

At least 19 recordsLinked to original sources

arXiv2013

Mass hierarchy, 2-3 mixing and CP-phase with Huge Atmospheric Neutrino Detectors

We explore the physics potential of multi-megaton scale ice or water Cherenkov detectors with low ($\sim 1$ GeV) threshold. Using some proposed characteristics of the PINGU detector setup we compute the distributions of events versus neutrino energy $E_ν$ and zenith angle $θ_z$, and study their dependence on yet unknown neutrino parameters. The $(E_ν- θ_z)$ regions are identified where the distributions have the highest sensitivity to the neutrino mass hierarchy, to the deviation of the 2-3 mixing from the maximal one and to the CP-phase. We evaluate significance of the measurements of the neutrino parameters and explore dependence of this significance on the accuracy of reconstruction of the neutrino energy and direction. The effect of degeneracy of the parameters on the sensitivities is also discussed. We estimate the characteristics of future detectors (energy and angle resolution, volume, etc.) required for establishing the neutrino mass hierarchy with high confidence level. We find that the hierarchy can be identified at $3σ$ -- $10σ$ level (depending on the reconstruction accuracies) after 5 years of PINGU operation.

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arXiv2012

Neutrino production coherence and oscillation experiments

Neutrino oscillations are only observable when the neutrino production, propagation and detection coherence conditions are satisfied. In this paper we consider in detail neutrino production coherence, taking π\to μν\ decay as an example. We compare the oscillation probabilities obtained in two different ways: (1) coherent summation of the amplitudes of neutrino production at different points along the trajectory of the parent pion; (2) averaging of the standard oscillation probability over the neutrino production coordinate in the source. We demonstrate that the results of these two different approaches exactly coincide, provided that the parent pion is considered as pointlike and the detection process is perfectly localized. In this case the standard averaging of the oscillation probability over the finite spatial extensions of the neutrino source (and detector) properly takes possible decoherence effects into account. We analyze the reason for this equivalence of the two approaches and demonstrate that for pion wave packets of finite width σ_{xπ} the equivalence is broken. The leading order correction to the oscillation probability due to σ_{xπ}\ne 0 is shown to be \sim [v_g/(v_g-v_π)]σ_{xπ}/l_{osc}, where v_g and v_π\ are the group velocities of the neutrino and pion wave packets, and l_{osc} is the neutrino oscillation length.

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arXiv2010

Neutrino oscillations: Entanglement, energy-momentum conservation and QFT

We consider several subtle aspects of the theory of neutrino oscillations which have been under discussion recently. We show that the $S$-matrix formalism of quantum field theory can adequately describe neutrino oscillations if correct physics conditions are imposed. This includes space-time localization of the neutrino production and detection processes. Space-time diagrams are introduced, which characterize this localization and illustrate the coherence issues of neutrino oscillations. We discuss two approaches to calculations of the transition amplitudes, which allow different physics interpretations: (i) using configuration-space wave packets for the involved particles, which leads to approximate conservation laws for their mean energies and momenta; (ii) calculating first a plane-wave amplitude of the process, which exhibits exact energy-momentum conservation, and then convoluting it with the momentum-space wave packets of the involved particles. We show that these two approaches are equivalent. Kinematic entanglement (which is invoked to ensure exact energy-momentum conservation in neutrino oscillations) and subsequent disentanglement of the neutrinos and recoiling states are in fact irrelevant when the wave packets are considered. We demonstrate that the contribution of the recoil particle to the oscillation phase is negligible provided that the coherence conditions for neutrino production and detection are satisfied. Unlike in the previous situation, the phases of both neutrinos from $Z^0$ decay are important, leading to a realization of the Einstein-Podolsky-Rosen paradox.

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arXiv2008

An accurate analytic description of neutrino oscillations in matter

A simple closed-form analytic expression for the probability of two-flavour neutrino oscillations in a matter with an arbitrary density profile is derived. Our formula is based on a perturbative expansion and allows an easy calculation of higher order corrections. The expansion parameter is small when the density changes relatively slowly along the neutrino path and/or neutrino energy is not very close to the Mikheyev-Smirnov-Wolfenstein (MSW) resonance energy. Our approximation is not equivalent to the adiabatic approximation and actually goes beyond it. We demonstrate the validity of our results using a few model density profiles, including the PREM density profile of the Earth. It is shown that by combining the results obtained from the expansions valid below and above the MSW resonance one can obtain a very good description of neutrino oscillations in matter in the entire energy range, including the resonance region.

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arXiv2006

Neutrino oscillations: theory and phenomenology

A brief overview of selected topics in the theory and phenomenology of neutrino oscillations is given. These include: oscillations in vacuum and in matter; phenomenology of 3-flavour neutrino oscillations and effective 2-flavour approximations; CP and T violation in neutrino oscillations in vacuum and in matter; matter effects on ν_μ\leftrightarrow ν_τoscillations; parametric resonance in neutrino oscillations inside the earth; oscillations below and above the MSW resonance; unsettled issues in the theory of neutrino oscillations.

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arXiv2006

Duality in Left-Right Symmetric Seesaw Mechanism

We consider type I+II seesaw mechanism, where the exchanges of both right-handed neutrinos and isotriplet Higgs bosons contribute to the neutrino mass. Working in the left-right symmetric framework and assuming the mass matrix of light neutrinos $m_ν$ and the Dirac-type Yukawa couplings to be known, we find the triplet Yukawa coupling matrix $f$, which carries the information about the masses and mixing of the right-handed neutrinos. We show that in this case there exists a duality: for any solution $f$, there is a dual solution $\hat{f}=m_ν/v_L-f$, where $v_L$ is the VEV of the triplet Higgs. Thus, unlike in pure type I (II) seesaw, there is no unique allowed structure for the matrix $f$. For $n$ lepton generations the number of solutions is $2^n$. We develop an exact analytic method of solving the seesaw non-linear matrix equation for $f$.

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arXiv2005

Oscillations of high energy neutrinos in matter: Precise formalism and parametric resonance

We present a formalism for precise description of oscillation phenomena in matter at high energies or high densities, V > Δm^2/2E, where V is the matter-induced potential of neutrinos. The accuracy of the approximation is determined by the quantity \sin^2 2θ_m ΔV/2πV, where θ_m is the mixing angle in matter and ΔV is a typical change of the potential over the oscillation length (l \sim 2π/V). We derive simple and physically transparent formulas for the oscillation probabilities, which are valid for arbitrary matter density profiles. They can be applied to oscillations of high energy (E > 10 GeV) accelerator, atmospheric and cosmic neutrinos in the matter of the Earth, substantially simplifying numerical calculations and providing an insight into the physics of neutrino oscillations in matter. The effect of parametric enhancement of the oscillations of high energy neutrinos is considered. Future high statistics experiments can provide an unambiguous evidence for this effect.

hep-ph↗

arXiv2005

Geotomography with solar and supernova neutrinos

We show how by studying the Earth matter effect on oscillations of solar and supernova neutrinos inside the Earth one can in principle reconstruct the electron number density profile of the Earth. A direct inversion of the oscillation problem is possible due to the existence of a very simple analytic formula for the Earth matter effect on oscillations of solar and supernova neutrinos. From the point of view of the Earth tomography, these oscillations have a number of advantages over the oscillations of the accelerator or atmospheric neutrinos, which stem from the fact that solar and supernova neutrinos are coming to the Earth as mass eigenstates rather than flavour eigenstates. In particular, this allows reconstruction of density profiles even over relatively short neutrino path lengths in the Earth, and also of asymmetric profiles. We study the requirements that future experiments must meet to achieve a given accuracy of the tomography of the Earth.

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arXiv2004

A simple analytic three-flavour description of the day-night effect in the solar neutrino flux

In the 3-flavour framework we derive a simple approximate analytic expression for the day-night difference of the flux of solar $ν_e$ at terrestrial detectors which is valid for an arbitrary Earth density profile. Our formula has the accuracy of a few per cent and reproduces all the known analytic expressions for the Earth matter effects on the solar neutrino oscillations obtained under simplifying assumptions about the Earth's density profile (matter of constant density, 3 layers of constant densities, and adiabatic approximation). It can also be used for studying the Earth matter effects on the oscillations of supernova neutrinos. We also discuss the possibility of probing the leptonic mixing angle $θ_{13}$ through day--night asymmetry measurements at future water Cherenkov solar neutrino detectors. We show that, depending on the measured value of the asymmetry, the current upper bound on $θ_{13}$ may be improved, or even a lower bound on this mixing parameter may be obtained.

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arXiv2002

Solar neutrino oscillations and bounds on neutrino magnetic moment and solar magnetic field

If the observed deficit of solar neutrinos is due to neutrino oscillations, neutrino conversions caused by the interaction of their transition magnetic moments with the solar magnetic field (spin-flavour precession) can still be present at a subdominant level. In that case, the combined action of neutrino oscillations and spin-flavour precession can lead to a small but observable flux of electron antineutrinos coming from the sun. Non-observation of these nuebar's could set limits on neutrino transition moment μand the strength and coordinate dependence of the solar magnetic field B_\perp. The sensitivity of the nuebar flux to the product μB_\perp is strongest in the case of the vacuum oscillation (VO) solution of the solar neutrino problem; in the case of the LOW solution, it is weaker, and it is the weakest for the LMA solution. For different solutions, different characteristics of the solar magnetic field B_\perp(r) are probed: for the VO solution, the nuebar flux is determined by the integral of B_\perp(r) over the solar convective zone, for LMA it is determined by the magnitude of B_\perp in the neutrino production region, and for LOW it depends on the competition between this magnitude and the derivative of B_\perp(r) at the surface of the sun.

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arXiv2002

Neutrino oscillations beyond two flavours

I review some theoretical aspects of neutrino oscillations in the case when more than two neutrino flavours are involved. These include: approximate analytic solutions for 3-flavour (3f) oscillations in matter; matter effects in nu_mu - nu_tau oscillations; 3f effects in oscillations of solar, atmospheric, reactor and supernova neutrinos and in accelerator long-baseline experiments; CP and T violation in neutrino oscillations in vacuum and in matter; the problem of U_{e3}; 4f oscillations.

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arXiv2002

Vacuum energy and relativistic invariance

It is argued that the zero-point energies of free quantum fields diverge at most quadratically and not quartically, as is generally believed. This is a consequence of the relativistic invariance which requires that the energy density of the vacuum $ρ$ and its pressure $p$ satisfy $ρ=-p$. The usually obtained quartic divergence is an artifact of the use of a noninvariant regularization which violates this relation. One consequence of our results is that the zero-point energies of free massless fields vanish. Implications for the cosmological constant problem are briefly discussed.

hep-th↗

arXiv2002

Supernova neutrinos: difference of nu_mu - nu_tau fluxes and conversion effects

The formalism of flavor conversion of supernova neutrinos is generalized to include possible differences in the fluxes of the muon and tau neutrinos produced in the star. In this case the radiatively induced difference of the nu_mu and nu_tau potentials in matter becomes important. The nu_mu and nu_tau flux differences can manifest themselves in the effects of the Earth matter on the observed nu_e (antinu_e) signal if: (i) the neutrino mass hierarchy is normal (inverted); (ii) the solution of the solar neutrino problem is in the LMA region; (iii) the mixing U_{e3} is relatively large: |U_{e3}|>10^{-3}. We find that for differences in the nu_mu - nu_tau (antinu_mu - antinu_tau) average energies and/or integrated luminosities < 20 %, the relative deviation of the observed nu_e (antinu_e) energy spectrum at E > 50 MeV from that in the case of the equal fluxes can reach 20 - 30 % (10 - 15 %) for neutrinos crossing the Earth. It could be detected in future if large detectors sensitive to the nu_e (antinu_e) energy spectrum become available. The study of this effect would allow one to test the predictions of the nu_mu, nu_tau, antinu_mu, antinu_tau fluxes from supernova models and therefore give an important insight into the properties of matter at extreme conditions. It should be taken into account in the reconstruction of the neutrino mass spectrum and mixing matrix from the supernova neutrino observations. We show that even for unequal nu_mu and nu_tau fluxes, effects of leptonic CP violation can not be studied in the supernova neutrino experiments.

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arXiv2002

Distinguishing magnetic moment from oscillation solutions of the solar neutrino problem with Borexino

Assuming that the observed deficit of solar neutrinos is due to the interaction of their transition magnetic moment with the solar magnetic field we derive the predictions for the forthcoming Borexino experiment. Three different model magnetic field profiles which give very good global fits of the currently available solar neutrino data are used. The expected signal at Borexino is significantly lower than those predicted by the LMA, LOW and VO neutrino oscillation solutions of the solar neutrino problem. It is similar to that of the SMA oscillation solution which, however, is strongly disfavoured by the Super-Kamiokande data on day and night spectra and zenith angle distribution of the events. Thus, the neutrino magnetic moment solution of the solar neutrino problem can be unambiguously distinguished from the currently favoured oscillation solutions at Borexino.

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arXiv2001

Dynamical localization of gauge fields on a brane

We propose a dynamical mechanism of localization of gauge fields on a brane in which gauge bosons are excitations of the brane itself or composites made out of matter fields localized on the brane. The mechanism is operative for both Abelian and non-Abelian gauge fields. Several scalar and scalar-fermion composite models of gauge fields are considered. The models exhibit exact gauge invariance and therefore charge universality of gauge interactions is automatically preserved. The mechanism is shown to be equivalent to a modification of the Dvali, Gabadadze and Shifman scenario in which gauge bosons have no bulk kinetic terms and only possess induced kinetic terms on the brane.

hep-th↗

arXiv2001

T violation in neutrino oscillations in matter

We consider the interplay of fundamental and matter-induced T violation effects in neutrino oscillations in matter. After discussing the general features of these effects we derive a simple approximate analytic expression for the T-violating probability asymmetry ΔP^T_{ab} for three-flavour neutrino oscillations in a matter with an arbitrary density profile in terms of the two-flavour neutrino amplitudes. Explicit examples are given for the cases of a two-layer medium and for the adiabatic limit in the general case. We then discuss implications of the obtained results for long baseline experiments. We show, in particular, that asymmetric matter effects cannot hinder the determination of the fundamental CP and T-violating phase δ_{CP} in the long baseline experiments as far as the error in this determination is larger than 1% at 99% C.L. Since there are no T-violating effects in the two-flavour case, and in the limits of vanishing θ_{13} or Δm_{21}^2 the three-flavour neutrino oscillations effectively reduce to the two-flavour ones, studying the T-violating asymmetries ΔP^T_{ab} can in principle provide us with a complementary means of measuring θ_{13} and Δm_{21}^2.

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arXiv2001

Matter effects in oscillations of neutrinos traveling short distances in matter

It is well known that when the distance $t$ traveled by neutrinos in matter is short, matter effects in oscillations of neutrino flavour are small and decrease with decreasing $t$ more rapidly than the oscillations effects themselves. We discuss the reason for this and demonstrate that under certain circumstances this statement is no longer correct. In particular, we show that if neutrinos propagate significant distances in vacuum before entering matter (or after exiting it), matter effects in short-$t$ neutrino oscillations can be significantly enhanced. Implications for oscillations of solar and atmospheric neutrinos with nearly horizontal trajectories inside the earth and for accelerator experiments are considered. We also comment on neutrino oscillations in matter due to flavour changing neutral currents.

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arXiv2000

News about nu's

We review new results in neutrino physics, including the latest data of the Super-Kamiokande, SNO and K2K experiments.

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