16383510
Lepton mixing: Small, large, maximal?
The SuperKamiokande data on atmospheric neutrinos imply that $\nu_{\mu}$ 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.
115887973
Solar neutrinos: Theoretical aspects
18492548
Pontecorvo's original oscillations revisited
Abstract We show that a left-handed neutrino ν L can oscillate into its CPT -conjugate state ν R with maximal amplitude, in direct analogy with K 0 − K 0 oscillations. Peculiarities of such oscillations under different conditions are studied.
59164737
Recent developments in neutrino phenomenology
The first phase of studies of the neutrino mass and mixing is essentially over. The outcome is the discovery of non-zero neutrino mass and determination of the dominant structure of the lepton mixing matrix. In some sense this phase was very simple, and nature was very collaborative with us: Two main effects - the vacuum oscillations and the adiabatic conversion in matter (the MSW-effect) - provide complete interpretation of the experimental results. Furthermore, with the present accuracy of measurements the $3\nu-$mixing analysis is essentially reduced to the $2\nu$ consideration. I will present a concise and comprehensive description of this first phase. The topics include: (i) the concept of neutrino mixing in vacuum and matter; (ii) physics of the oscillations and adiabatic conversion; (iii) the experimental evidences of the flavor transformations and determination of the oscillation parameters. Some implications of the obtained results are discussed. Comments are given on the next phase of the field that will be much more involved.
31519375
Multiple spectral splits of supernova neutrinos.
Collective oscillations of supernova neutrinos swap the spectra f(nu(e))(E) and f(nu[over ](e))(E) with those of another flavor in certain energy intervals bounded by sharp spectral splits. This phenomenon is far more general than previously appreciated: typically one finds one or more swaps and accompanying splits in the nu and nu[over ] channels for both inverted and normal neutrino mass hierarchies. Depending on an instability condition, swaps develop around spectral crossings (energies where f(nu(e))=f(nu(x)), f(nu[over ](e))=f(nu[over ](x)) as well as E-->infinity where all fluxes vanish), and the widths of swaps are determined by the spectra and fluxes. Washout by multiangle decoherence varies across the spectrum and splits can survive as sharp spectral features.
119540272
Self-induced spectral splits in supernova neutrino fluxes
In the dense-neutrino region above the neutrino sphere of a supernova (r < or approx. 400 km), neutrino-neutrino refraction causes collective flavor transformations. They can lead to 'spectral splits' where an energy E{sub split} splits the transformed spectrum sharply into parts of almost pure but different flavors. Unless there is an ordinary MSW resonance in the dense-neutrino region, E{sub split} is determined by flavor-lepton number conservation alone. Spectral splits are created by an adiabatic transition between regions of large and small neutrino density. We solve the equations of motion in the adiabatic limit explicitly and provide analytic expressions for a generic example.
18803649
Low-energy moments of heavy quark current correlators at four loops
Abstract We describe several techniques for the calculation of multi-loop integrals and their application to heavy quark current correlators. As new results, we present the four-loop correction to the second and third physical moments in the low-energy expansions of vector, axial-vector and scalar quark current correlators. Using the Ward identity, we obtain the third and fourth moments for the pseudo-scalar correlator. We briefly discuss the impact of these results on the determination of the charm quark mass and the strong coupling constant using lattice simulations for the current correlators and of the charm- and bottom-quark mass from experimental data for σ ( e + e − → hadrons ) .
120006374
Contributions of scalar leptoquarks to the cross sections for the production of quark-antiquark pairs in electron-positron annihilation
AbstractThe contributions of scalar-leptoquark doublets to the cross sections 
$$\sigma _{Q\tilde Q} $$
, for the production of quark-antiquark pairs in electron-positron annihilation are calculated within the minimal model based on the four-color symmetry of quarks and leptons. These contributions are analyzed versus the scalar-leptoquark masses and the mixing parameters of the model at colliding-particle energies in the range 250–1000 GeV. It is shown that the contributions in question are of greatest importance for processes leading to t-quark production. In particular, it is found that, with allowance for the contribution of the scalar leptoquark of charge 5/3 and mass in the range 250–500 GeV, the cross section 
$$\sigma _{t\tilde t} $$
 calculated at a mixing-parameter value of kt ∼ 1 may be severalfold larger than the corresponding cross section 
$$\sigma _{t\tilde t}^{(SM)} $$
 within the Standard Model. The possibility of setting constraints on the scalar-leptoquark masses and on the mixing parameters by measuring such contributions at future electron-positron colliders is indicated.
9034286
Geometric approach to asymptotic expansion of Feynman integrals
We present an algorithm that reveals relevant contributions in non-threshold-type asymptotic expansion of Feynman integrals about a small parameter. It is shown that the problem reduces to finding a convex hull of a set of points in a multidimensional vector space.
116859657
Scalar Leptoquark Contributions into $l_i\to l_j\gamma$ Processes
The contributions of scalar leptoquarks in lepton flavor violating (LFV) processes of type $l_i\to l_j \gamma$ are investigated in frame of the minimal model with the four color symmetry and Higgs mechanism of quark and lepton mass generation. It is shown that experimental data on the decays $\mu\to e \gamma$, $\tau \to \mu \gamma$, $\tau\to e \gamma$ allow the existence of light scalar leptoquarks of type under consideration, with masses of order 1 TeV or below.
120577993
Asymptotic behavior of amplitudes for longitudinal-leptoquark processes and structure of the scalar sector in the minimal model involving four-color symmetry
Within the minimal model based on the four-color symmetry of quarks and leptons of the Pati-Salam type, the asymptotic behavior of amplitudes for processes involving longitudinal leptoquarks (and W or Z′ bosons) is investigated, together with the mechanism according to which the growth of these amplitudes at high energies is suppressed by scalar fields. It is shown that, within the Higgs mechanism of mass generation and of the mass splitting of quarks and leptons, the four-color symmetry of quarks and leptons requires that scalar-leptoquark doublets, scalar-gluon doublets, and an extra color-singlet scalar doublet exist in addition to the standard Higgs doublet.