18100102
Reconstructing neutrino mass spectrum
Reconstruction of the neutrino mass spectrum and lepton mixing is one of the fundamental problems of particle physics. In this connection we consider two central topics: (i) the origin of large lepton mixing, (ii) possible existence of new (sterile) neutrino states. We discuss also possible relation between large mixing and existence of sterile neutrinos.
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.
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.
115887973
Solar neutrinos: Theoretical aspects
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.
118355424
Chiral color symmetry and $G'$-boson mass limit from Tevatron data on $t \bar t$-production
A gauge model with chiral color symmetry of quarks is considered and possible effects of the color $G'$-boson octet predicted by this symmetry are investigated. The contributions of the $G'$-boson to the cross section $\sigma_{t\bar{t}}$ and to the forward-backward asymmetry $A_{\rm FB}^{p \bar p}$ of $t\bar{t}$ production at the Tevatron are calculated and analysed in dependence on two free parameters of the model, the mixing angle $\theta_G$ and $G'$ mass $m_{G'}$. The $G'$-boson contributions to $\sigma_{t\bar{t}}$ and $A_{\rm FB}^{p \bar p}$ are shown to be consistent with the Tevatron data on $\sigma_{t\bar{t}}$ and $A_{\rm FB}^{p \bar p}$, the allowed region in the $m_{G'} - \theta_G$ plane is discussed and around $m_{G'}=1.2 \, TeV, \; \theta_G=14^\circ $ the region of $1 \sigma$ consistency is found.
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.
15966773
Fermionic contributions to the three-loop static potential
Abstract We consider the three-loop corrections to the static potential which are induced by a closed fermion loop. For the reduction of the occurring integrals a combination of the Grobner and Laporta algorithm has been used and the evaluation of the master integrals has been performed with the help of the Mellin–Barnes technique. The fermionic three-loop corrections amount to 2% of the tree-level result for top quarks, 8% for bottom quarks and 27% for the charm quark system.
58945450
Optical measurement of transverse laser cooling with synchro-betatron coupling
Laser cooling experiment of transverse direction for Mg is performed at the small ion storage and cooler ring, S-LSR. We measured horizontal beam size with CCD camera, and longitudinal momentum spread with PAT (Post Acceleration Tube). The measured beam size with CCD camera is decreased from about 1mm to 0.55mm and longitudinal momentum spread measured with PAT increased near the resonant condition. This suggests transverse temperature was transferred to longitudinal direction with synchro-betatron coupling. INTRODUCTION There are several methods to cool ion beam, such as stochastic cooling, electron beam cooling, and laser cooling. Among these methods, laser cooling can achieve the lowest temperature due to its very strong cooling force. The first experiment of laser cooling of ion beam was carried out at TSR [1], and followed at ASTRID [2]. In laser cooling method, a laser is co-propagating or counter-propagating with the ion beam. Since momentum transfer between the laser and the ion beam occurs longitudinally, we can cool the beam particles mainly in the longitudinal direction. Although intra-beam scattering cools the beam transversely, cooling power is weak in usual particle density [3]. Resonant coupling method is proposed to cool ion beam transversely [4]. In the cases betatron tunes (νx, νy) and synchrotron tune νs have the following relations, νs νx = integer νx νy = integer, and there is energy change at a position with a finite dispersion, laser cooling power transmits to transverse direction. In a storage ring, if cooling power is stronger than heating power, beam will be cooled 3-dimensinally. To realize such beam crystallization, the lattice must be properly designed. A small laser-equipped storage ring (SLSR) (Fig. 1) was constructed for this purpose [5]. The principal parameters of S-LSR, the beam and the laser used in the experiment are shown in Table 1.