Evgeny Kh. Akhmedov

Series expansions for three flavor neutrino oscillation probabilities in matter

We present a number of complete sets of series expansion formulas for neutrino oscillation probabilities in matter of constant density for three flavors. In particular, we study expansions in the mass hierarchy parameter α≡Δm212/Δm312 and mixing parameter s13≡sin θ13 up to second order and expansions only in α and only in s13 up to first order. For each type of expansion we also present the corresponding formulas for neutrino oscillations in vacuum. We perform a detailed analysis of the accuracy of the different sets of series expansion formulas and investigate which type of expansion is most accurate in different regions of the parameter space spanned by the neutrino energy E, the baseline length L, and the expansion parameters α and s13. We also present the formulas for series expansions in α and in s13 up to first order for the case of arbitrary matter density profiles. Furthermore, it is shown that in general all the 18 neutrino and antineutrino oscillation probabilities can be expressed through just two independent probabilities.

Probing the seesaw mechanism with neutrino data and leptogenesis

We use the current low-energy neutrino data to understand the structure of the neutrino mass matrix. Considering this information and assuming hierarchical neutrino Yukawa couplings, we use the seesaw formula to study the properties of the heavy right-handed neutrinos Ni. We find that successful baryogenesis via leptogenesis requires mass degeneracy and maximal mixing of N1 and N2.

Left-right symmetry breaking in NJL approach

Abstract We study left-right symmetric models which contain only fermion and gauge boson fields and no elementary scalars. The Higgs bosons are generated dynamically through a set of gauge- and parity-invariant 4-fermion operators. It is shown that in a model with a composite bi-doublet and two triplet scalars there is no parity breaking at low energies, whereas in the model with two doublets instead of two triplets parity is broken automatically regardless of the choice of the parameters of the model. For phenomenologically allowed values of the right-handed scale a tumbling symmetry breaking mechanism is realized in which parity breaking at a high scale μ R propagates down and eventually causes the electro-weak symmetry breaking at the scale μ EW ∼ 100 GeV. The model exhibits a number of low and intermediate mass Higgs bosons with certain relations between their masses. In particular, the components of the SU (2) L Higgs doublet χ L are pseudo-Goldstone bosons of an accidental (approximate) SU (4) symmetry of the Higgs potential and therefore are expected to be relatively light.

T violation in neutrino oscillations in matter

Abstract 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 ΔPTab 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 δCP in the long baseline experiments as far as the error in this determination is larger than 1% at 99% CL. Since there are no T-violating effects in the two-flavour case, and in the limits of vanishing θ13 or Δm212 the three-flavour neutrino oscillations effectively reduce to the two-flavour ones, studying the T-violating asymmetries ΔPTab can in principle provide us with a complementary means of measuring θ13 and Δm212.

Improving Electro-Weak Fits with TeV-scale Sterile Neutrinos

A bstractWe study the impact of TeV-scale sterile neutrinos on electro-weak precision observables and lepton number and flavour violating decays in the framework of a type-I see-saw extension of the Standard Model. At tree level sterile neutrinos manifest themselves via non-unitarity of the PMNS matrix and at one-loop level they modify the oblique radiative corrections. We derive explicit formulae for the S, T, U parameters in terms of the neutrino masses and mixings and perform a numerical fit to the electro-weak observables. We find regions of parameter space with a sizable active-sterile mixing which provide a better over-all fit compared to the case where the mixing is negligible. Specifically we find improvements of the invisible Z-decay width, the charged-to-neutral-current ratio for neutrino scattering experiments and of the deviation of the W boson mass from the theoretical expectation.

MiniBooNE and LSND data: non-standard neutrino interactions in a (3+1) scheme versus (3+2) oscillations

The recently observed event excess in MiniBooNE anti-neutrino data is in agreement with the LSND evidence for electron anti-neutrino appearance. We propose an explanation of these data in terms of a (3+ 1) scheme with a sterile neutrino including non-standard neutrino interactions (NSI) at neutrino production and detection. The interference between oscillations and NSI provides a source for CP violation which we use to reconcile different results from neutrino and anti-neutrino data. Our best fit results imply NSI at the level of a few percent relative to the standard weak interaction, in agreement with current bounds. We compare the quality of the NSI fit to the one obtained within the (3+ 1) and (3+ 2) pure oscillation frameworks. We also briefly comment on using NSI (in an effective two-flavour framework) to address a possible difference in neutrino and anti-neutrino results from the MINOS experiment.

1-3 leptonic mixing and the neutrino oscillograms of the Earth

We develop a detailed and comprehensive description of neutrino oscillations driven by the 1-3 mixing in the matter of the Earth. The description is valid for the realistic (PREM) Earth density pro ...

Neutrino oscillations: quantum mechanics vs. quantum field theory

A consistent description of neutrino oscillations requires either the quantum-mechanical (QM) wave packet approach or a quantum field theoretic (QFT) treatment. We compare these two approaches to neutrino oscillations and discuss the correspondence between them. In particular, we derive expressions for the QM neutrino wave packets from QFT and relate the free parameters of the QM framework, in particular the effective momentum uncertainty of the neutrino state, to the more fundamental parameters of the QFT approach. We include in our discussion the possibilities that some of the neutrino’s interaction partners are not detected, that the neutrino is produced in the decay of an unstable parent particle, and that the overlap of the wave packets of the particles involved in the neutrino production (or detection) process is not maximal. Finally, we demonstrate how the properly normalized oscillation probabilities can be obtained in the QFT framework without an ad hoc normalization procedure employed in the QM approach.

Neutrino oscillograms of the Earth: Effects of 1-2 mixing and CP-violation

Submitted on 9 Apr 2008 (v1), last revised 18 Jun 2008 (this version, v4).-- 49 pages, LaTeX file using JHEP style, 13 figures included.-- Final version published in: JHEP06(2008)072, full-text available at: http://dx.doi.org/10.1088/1126-6708/2008/06/072.

Oscillations of Mössbauer neutrinos

We calculate the probability of recoilless emission and detection of neutrinos (Mossbauer effect with neutrinos) taking into account the boundedness of the parent and daughter nuclei in the neutrino source and detector as well as the leptonic mixing. We show that, in spite of their near monochromaticity, the recoillessly emitted and captured neutrinos oscillate. After a qualitative discussion of this issue, we corroborate and extend our results by computing the combined rate of e production, propagation and detection in the framework of quantum field theory, starting from first principles. This allows us to avoid making any a priori assumptions about the energy and momentum of the intermediate-state neutrino. Our calculation permits quantitative predictions of the transition rate in future experiments, and shows that the decoherence and delocalization factors, which could in principle suppress neutrino oscillations, are irrelevant under realistic experimental conditions.