119273437
Neutrino Masses and a Fourth Generation of Fermions
Abstract We study neutrino mass generation in models with four chiral families of leptons and quarks and four right handed neutrinos. Generically, in these models there are three different contributions to the light neutrino masses: the usual see-saw contribution, the tree-level contribution due to mixing of light neutrinos with neutrino of the fourth generation, and the two loop contribution due to the Majorana mass term of the fourth neutrino. We study properties of these contributions and their experimental bounds. The regions of the parameters (mixings of the fourth neutrino, masses of RH neutrino components, etc.) have been identified where various contributions dominate. New possibilities of a realisation of the flavour symmetries in the four family context are explored. In particular, we consider applications of the smallest groups, e.g. SG ( 20 , 3 ) , with irreducible representation 4 .
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.
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.
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.
115887973
Solar neutrinos: Theoretical aspects
123279554
Chiral color quark symmetry and possible constraints on the G′-boson mass from tevatron and LHC data
A gauge model featuring a chiral color symmetry of quarks was considered, and possible manifestations of this symmetry in proton-antiproton and proton-proton collisions at the Tevatron and LHC energies were studied. The cross section $$\sigma _{t\bar t}$$ for the production of $$t\bar t$$ quark pairs at the Tevatron and the forward-backward asymmetry $$A_{FB}^{p\bar p}$$ in this process were calculated and analyzed with allowance for the contributions of the G′-boson predicted by the chiral color symmetry of quarks, the G′-boson massmG′ and the mixing angle θG being treated as free parameters of the model. Limits on mG′ versus θG were studied on the basis of data from the Tevatron on $$\sigma _{t\bar t}$$ and $$A_{FB}^{p\bar p}$$, and the region compatible with these data within one standard deviation was found in the mG′-θG plane. The region ofmG′-mass values that is appropriate for observing the G′-boson at LHC is discussed.
17736206
BOUNDS ON SCALAR LEPTOQUARK MASSES FROM S, T, U PARAMETERS IN THE MINIMAL FOUR-COLOR QUARK-LEPTON SYMMETRY MODEL
Abstract The contributions into radiative correction parameters S , T , U from the scalar leptoquarks are calculated in the minimal gauge model with the four-color quark-lepton symmetry. It is shown that the contributions into T and U from the scalar leptoquark doublets are not positive definite. Using the current experimental data on S , T , U the bounds on the scalar leptoquark masses are obtained. In particular, the existence of the relatively light scalar leptoquark with electric charge 2/3 is shown to be compatible with the current experimental data on S , T , U .
118565164
Cross Section and Forward-Backward Asymmetry of $t\bar{t}$ Production in the Model with Four Color Symmetry
The contributions to the cross section $\sigma_{t\bar{t}}$ and to the forward-backward asymmetry $A_{\rm FB}^{t \bar t}$ of $t\bar{t}$ production at the Tevatron from $Z'$-boson and scalar leptoquarks $S^{(\pm)}_a$ and scalar gluons $F_a$ predicted by the minimal model with four color quark-lepton symmetry are calculated. These contributions are shown to be small in tree approximation and can be significant with account of the 1-loop $gt\bar{t}$ effective vertex induced by the scalar doublets. The lower mass limit for scalar gluons $m_F \gtrsim 320\, GeV$ from the Tevatron data is obtained and it is shown that for $m_{F_1}\lesssim 990\,GeV$ the scalar gluon $F_1$ can be evident at LHC at the significance not less that $3\sigma$ (for $\sqrt{s}=14$ TeV, $L=10\,fb^{-1}$).
41885673
Quark and gluon form factors to three loops.
We compute the form factors of the photon-quark-anti-quark vertex and the effective vertex of a Higgs-boson and two gluons to three-loop order within massless perturbative quantum chromodynamics. These results provide building blocks for many third-order cross sections. Furthermore, this is the first calculation of complete three-loop vertex corrections.
118835200
THE CHIRAL COLOR SYMMETRY OF QUARKS AND G′-BOSON CONTRIBUTIONS TO CHARGE ASYMMETRY IN $t \bar t$-PRODUCTION AT THE LHC AND TEVATRON
The contributions of G′-boson predicted by the chiral color symmetry of quarks to the charge asymmetry in -production at the LHC and to the forward–backward asymmetry in -production at the Tevatron are calculated and analyzed in dependence on two free parameters of the model, the G′ mass mG′ and mixing angle θG. The mG′ - θG regions of 1 σ consistency with the CMS data on the cross-section and on the charge asymmetry are found and compared with those resulted from the CDF data on the cross-section and on the forward–backward asymmetry of -production at the Tevatron with account of the current SM predictions for .