119354807
Neutrino masses and mixing: Singular mass matrices and quark lepton symmetry
Abstract We suggest an approach to explain the observed pattern of the neutrino masses and mixing which employs the weakly violated quark–lepton equality and does not require introduction of an ad hoc symmetry of the neutrino sector. The mass matrices are nearly equal for all quarks and leptons. They have very small determinant and hierarchical form with expansion parameter λ ∼ sin θ c ∼ m μ / m τ . The latter can be realized, e.g., in the model with U ( 1 ) family symmetry. The equality is violated at the ∼ λ 2 level. Large lepton mixing appears as a result of summation of the neutrino and charged lepton rotations which diagonalize corresponding mass matrices in contrast with the quark sector where the up quark and down quark rotations cancel each other. We show that the flip of the sign of rotation in the neutrino sector is a result of the seesaw mechanism which also enhances the neutrino mixing. In this approach one expects, in general, deviation of the 2-3 mixing from maximal, s 13 ∼ ( 1 – 3 ) λ 2 , hierarchical neutrino mass spectrum, and m e e 10 − 2 eV . The scenario is consistent with the thermal leptogenesis and (in SUSY context) bounds on lepton number violating processes, like μ → e γ .
115887973
Solar neutrinos: Theoretical aspects
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.
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.
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.
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.
1669343
Applying Gröbner bases to solve reduction problems for Feynman integrals
We describe how Grobner bases can be used to solve the reduction problem for Feynman integrals, i.e. to construct an algorithm that provides the possibility to express a Feynman integral of a given family as a linear combination of some master integrals. Our approach is based on a generalized Buchberger algorithm for constructing Grobner-type bases associated with polynomials of shift operators. We illustrate it through various examples of reduction problems for families of one- and two-loop Feynman integrals. We also solve the reduction problem for a family of integrals contributing to the three-loop static quark potential.
119247211
The static quark potential to three loops in perturbation theory
The static potential constitutes a fundamental quantity of Quantum Chromodynamics. It has recently been evaluated to three-loop accuracy. In this contribution we provide details on the calculation and present results for the 14 master integrals which contain a massless one-loop insertion.
118758893
Minimal four-color model with quark-lepton symmetry and constraints on the Z{prime}-boson mass
A minimal model with quark-lepton symmetry is considered. This model, which describes unified electroweak and strong interactions, is a minimal extension of the standard model that involves four-color symmetry of quarks and leptons. Predicted relations between the masses of leptoquarks and W{sup +-}, Z, and Z{prime} bosons are studied, and the contributions of an additional Z{prime} boson to the cross sections for e{sup +}e{sup -} annihilation and the asymmetry A{sub FB} at TRISTAN and LEP200 energies are analyzed. Experimental data are shown to be consistent with the existence of a relatively light Z{prime} boson associated with four-color quark-lepton symmetry. 12 refs., 3 figs., 1 tab.
16841546
Three-loop heavy quark potential ¤
We discuss the calculation of the three-loop corrections to the static potential of two heavy quarks.