Search for ν<Subscript>μ</Subscript> → ν<Subscript>τ</Subscript> oscillations in appearance mode in the OPERA experiment

The OPERA experiment at the underground Gran Sasso Laboratory (LNGS) has to perform the first detection of neutrino oscillations in appearance mode through the direct observation of ν_μ → ν_τ. The apparatus consists of a lead/emulsion-film target complemented by electronic detectors. It is placed in the high-energy, long-baseline CERN neutrino beam (CNGS) 730 km away from the neutrino source. Runs with CNGS neutrinos were successfully carried out in 2008–2009 with the first candidate event ν_μ → gv_τ recently detected.     

The OPERA experiment

The aim of the OPERA experiment is to provide unambiguous evidence for the ν _μ ↔ ν _τ oscillation by looking at the appearance of ν _τ in a pure ν _μ beam. This oscillation will be sought in the region of the oscillation parameters indicated by the atmospheric neutrino results. The experiment is part of the CNGS (CERN Neutrino beam to Gran Sasso) project. The ν μ beam produced at CERN will be sent towards the Gran Sasso underground laboratory, where the OPERA detector is under construction. The detector, the physics potential, and performance for neutrino oscillation studies including the subleading ν _μ ↔ ν _ε search are presented. The text was submitted by the author in English.     

On phase ordering behind the propagating front of a second-order transition

In a real system the heating is nonuniform, and a second-order phase transition to a broken-symmetry phase occurs by propagation of a temperature front. Two parameters, the cooling rate τ _Q and the transition front velocity ν _T determine the nucleation of topological defects. Depending on the relation of these parameters, two regimes are found: in the regime of fast propagation defects are created according to the Zurek scenario for the homogeneous case, while in the slow-propagation regime vortex formation is suppressed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 96–101 (10 January 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Prospects for the measurement of the structure of the coupling of a Higgs boson to weak gauge bosons in weak boson fusion with the ATLAS detector

The prospects for the measurement of the tensor structure of the vertex between a standard model Higgs boson and two weak gauge bosons using the distribution of the azimuthal angles between the two tagging jets in the weak boson fusion channel are studied in a Monte Carlo analysis using the fast simulation of the ATLAS detector. The decay channels H→τ⁺τ^-→ll+4ν, H→τ⁺τ^-→lh+3ν at m_H=120 GeV and H→W⁺W^-→llνν at m_H=160 GeV are used in the analysis. For a standard model Higgs boson it is found that purely anomalous couplings are expected to be excluded at a confidence level corresponding to 2σ or more at m_H=120 GeV and more than 5σ at m_H=160 GeV from 30 fb^-1 of data. With a value of 1 roughly reproducing the standard model cross section for a purely anomalous coupling, the standard deviation in a measurement of a contribution of a CP even anomalous coupling in addition to the standard model coupling is estimated to be 0.20 at m_H=120 GeV and 0.09 at m_H=160 GeV.     

On the flavor composition of the solar <Superscript>7</Superscript>Be neutrino

The flavor composition of the solar beryllium neutrino was analyzed using schemes that include the new (heavy) neutrino (ν₄) at a negligible angle of mixing with the light partners ν _e , ν_μ, and ν_τ.     

Analyticity constraints on the strangeness changing vector current and applications to τ→Kπν<Subscript>τ</Subscript> and τ→Kππν<Subscript>τ</Subscript>

We discuss matrix elements of the strangeness changing vector current using their relation, due to analyticity, with πK scattering in the P-wave. We take into account experimental phase-shift measurements in the elastic channel as well as results, obtained by the LASS collaboration, on the details of inelastic scattering, which show the dominance of two quasi-two-body channels at medium energies. The associated form factors are shown to be completely determined, up to one flavor symmetry breaking parameter, imposing boundary conditions at t=0 from chiral and flavor symmetries and at t→∞ from QCD. We apply the results to the τ→Kπν_τ and τ→Kππν_τ amplitudes and compare the former to recent high statistics results from B factories. PACS 11.55.Fv; 11.30.Rd; 11.30.Hv; 13.35.Dx     

Two superconducting phases in the d=3 Hubbard model

The phase diagram of the d=3 Hubbard model is calculated as a function of temperature and electron density 〈n_i〉, in the full range of densities between 0 and 2 electrons per site, using renormalization-group theory. An antiferromagnetic phase occurs at lower temperatures, at and near the half-filling density of 〈n_i〉= 1. The antiferromagnetic phase is unstable to hole or electron doping of at most 15%, yielding to two distinct“τ" phases: for large coupling U/t, one such phase occurs between 30–35% hole or electron doping, and for small to intermediate coupling U/t another such phase occurs between 10–18% doping. Both τ phases are distinguished by non-zero hole or electron hopping expectation values at all length scales. Under further doping, the τ phases yield to hole- or electron-rich disordered phases. We have calculated the specific heat over the entire phase diagram. The low-temperature specific heat of the weak-coupling τ phase shows an exponential decay, indicating a gap in the excitation spectrum, and a cusp singularity at the phase boundary. The strong-coupling τ phase, on the other hand, has a critical exponent α≈-1, and an additional peak in the specific heat above the transition temperature possibly indicating pair formation. In the limit of large Coulomb repulsion, the phase diagram of the tJ model is recovered.     

Flavor structure of the electroweak spectra of monoenergetic solar neutrinos scattered by electron

Electroweak and electromagnetic contributions to the spectrum of beryllium solar neutrinos scattered by an electron are investigated. The flavor structure of the electroweak spectrum with the content of electron neutrinos and admixture components ν _μ and ν _τ is analyzed.     

Extended spin waves in aperiodic ferromagnetic chains

In this work, a one-dimensional quantum Heisenberg ferromagnet with aperiodic exchange couplings is considered. To produce an aperiodic distribution of exchange couplings, it is used a sinusoidal function whose phase φ varies as a power-law, φ∝n^ν, where n labels the positions along the chain. By using exact diagonalization, the spin-wave participation number and the local density of states are computed. The numerical calculations indicate that for 0 < ν < 1, this ferromagnetic system displays a phase of extended spin waves in the low-energy region. For ν > 1 all spin waves are localized except for the zero energy mode. By integrating the time-dependent Schr?dinger equation, the temporal evolution of the mean-square displacement of the wave-packet was followed. Associated with the emergence of extended spin waves, it was observed that the wave-packet mean-square displacement displays a ballistic spread.     

Cylindrical solitons in shallow water of variable depth

Summary The propagation and the interaction of cylindrical solitons in shallow vater of variable depth are studied. Starting from the cylindrically symmetric version of the equations describing long waves in a beach, a Korteweg-de Vries equation type ψ_τ+6ψψ_ξ+ψ_ξξξ=−Γ(τ)ψ is derived. Since no exact analytical solution has been found to date for this equation, some remarkable cases in which the equation takes up a tractable form are analysed. Finally the interaction between cylindrical imploding and expanding waves is considered and the phase shifts caused by the head-on collision are given. This work was supported by CNR-GNFM.     

d = 3 anisotropic and d = 2 tJ models: phase diagrams, thermodynamic properties, and chemical potential shift

The anisotropic d=3 tJ model is studied by renormalization-group theory, yielding the evolution of the system as interplane coupling is varied from the isotropic three-dimensional to quasi-two-dimensional regimes. Finite-temperature phase diagrams, chemical potential shifts, and in-plane and interplane kinetic energies and antiferromagnetic correlations are calculated for the entire range of electron densities. We find that the novel τ phase, seen in earlier studies of the isotropic d=3 tJ model, persists even for strong anisotropy. While the τ phase appears at low temperatures at 30–35% hole doping away from 〈 n_i〉=1, at smaller hole dopings we see a complex lamellar structure of antiferromagnetic and disordered regions, with a suppressed chemical potential shift, a possible marker of incommensurate ordering in the form of microscopic stripes. An investigation of the renormalization-group flows for the isotropic two-dimensional tJ model also shows a clear pre-signature of the τ phase, which in fact appears with finite transition temperatures upon addition of the smallest interplane coupling.     

Universal 23 symmetry

The possible maximal mixing seen in the oscillations of atmospheric neutrinos has led to the postulate of μ–τ symmetry, which interchanges ν_μ and ν_τ. We argue that such a symmetry need not be special to neutrinos but can be extended to all fermions. The assumption that all fermion mass matrices are approximately invariant under the interchange of the second and the third generation fields is shown to be phenomenologically viable and has interesting consequences. In the quark sector, the smallness of V_ub and V_cb can be consequences of this approximate 2–3 symmetry. The same approximate symmetry can simultaneously lead to a large atmospheric mixing angle and can describe the leptonic mixing quite well. We identify two generic scenarios leading to this. One is based on the conventional type-I seesaw mechanism and the other follows from the type-II seesaw model. The latter requires a quasi-degenerate neutrino spectrum for obtaining large atmospheric neutrino mixing in the presence of an approximate μ–τ symmetry. PACS 12.15.Ef; 14.60.Pq; 11.30.Er; 11.30.Qc     

Relationships between a microscopic parameter and the stochastic equations for interface's evolution of two growth models

The relationship between a microscopic parameter p, that is related to the probability of choosing a mechanism of deposition, and the stochastic equation for the interface's evolution is studied for two different models. It is found that in one model, that is similar to ballistic deposition, the corresponding stochastic equation can be represented by a Kardar-Parisi-Zhang (KPZ) equation where both λ and ν depend on p in the following way: ν(p) = νp and λ(p) = λp ^3/2. Furthermore, in the other studied model, which is similar to random deposition with relaxation, the stochastic equation can be represented by an Edwards-Wilkinson (EW) equation where ν depends on p according to ν(p) = νp ². It is expected that these results will help to find a framework for the development of stochastic equations starting from microscopic details of growth models. Received 26 August 2002 / Received in final form 20 November 2002 Published online 6 March 2003 RID="a" ID="a"e-mail: ealbano@inifta.unlp.edu.ar     

Universal magnetoluminescence kinetics in magnetically frozen 2D electron systems

The kinetics of recombination of electrons and acceptor-bound holes in AlGaAs-GaAs heterostructure obey a single-exponential decay in the liquid phase of 2D electrons, whereas localization gives rise to a broad spectrum of recombination rates, especially in the magnetic freeze-out regime. This results in a power-law dependence I(t)∝(τ/t)^α in the tail of the recombination kinetics, with the universal exponent α=(1−ν)⁻¹ at ν<1 for all the samples examined experimentally in this work. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 118–122 (25 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Results from Super-Kamiokande and K2K

Results from Super-Kamiokande-I’s entire 1496 live days of solar neutrino data are presented, including the absolute flux, energy spectrum, zenith angle (day/night) and seasonal variation. The possibility of MSW and vacuum oscillations is discussed in light of these results. Results from the first 1289 days of Super-K-I’s atmospheric neutrino analysis are also presented, including the evidence for ν_μ →ν _τ oscillations, against ν_μ → ν_sterile oscillations, and the current limits on proton decay. Finally, results based on 56 × 10¹⁹ protons on target are given for the K2K long-baseline neutrino oscillation experiment.     

S<Subscript>3</Subscript> symmetry and neutrino masses and mixings

Based on the universal seesaw mass matrix model with the three scalars φ_i, and by assuming S₃ flavor symmetry for the Yukawa interactions, the lepton masses and mixings are investigated systematically. In order to understand the observed neutrino mixing, the charged leptons (e,μ,τ) are regarded as the three objects (e₁,e₂,e₃) of S₃, while the neutrino mass eigenstates are regarded as the irreducible representation (ν_η,ν_σ,ν_π) of S₃, where (ν_π,ν_η) and ν_σ are a doublet and a singlet, respectively, which are composed of the three objects (ν₁,ν₂,ν₃) of S₃.     

The τ→μν<Subscript>i</Subscript>̄ν<Subscript>i</Subscript> decay in the Randall–Sundrum background with localized U(1)<Subscript>Y</Subscript> gauge boson

We study the effects of localization of the U(1)_Y gauge boson around the visible brane and the contributions of the Kaluza–Klein modes of Z bosons on the branching ratio of the lepton flavor violating τ→μν_īν_i decay. We observe that the branching ratio is sensitive to the amount of localization of the Z boson in the bulk of the Randall–Sundrum background.     

Remarks to the standard scheme (theory) of neutrino oscillations. Corrected scheme of neutrino oscillations

In the standard theory of neutrino oscillations, it is supposed that physically observed neutrino states ν _e , ν_μ, ν_τ, have no definite masses, that they are initially produced as a mixture of the ν₁, ν₂, ν₃ neutrino states (i.e., they are produced as a wave packet), and that neutrino oscillations are the real ones. Then, this wave packet must decompose at a definite distance into constituent parts and neutrino oscillations must disappear. It was shown that these suppositions lead to violation of the law of energy and momentum conservation. An alternative scheme of neutrino oscillations obtained within the framework of particle physics has been considered, where the above mentioned shortcomings are absent, the oscillations of neutrinos with equal masses are the real ones, and the oscillations of neutrinos with different masses are the virtual ones. Expressions for probabilities of neutrino transitions (oscillations) in the alternative (corrected) scheme are given. The text was submitted by the author in English.     

A chiral anomaly channel in τ-decay. II

The decay rate for τ→νηππ is calculated from an amplitude that has the chiral anomaly term as low-energy constraint and has realistic vectormeson meson pole continuation to physical energies. Work supported in part by the US Department of Energy under grant DOE/ER/01545 Supported by Bundesministerium für Forschung und Technologie, 05 4HH 92P/3, Bonn, FRG     

BCS-BEC crossover and quantum hydrodynamics in <Emphasis Type="Italic">p</Emphasis>-wave superfluids with a symmetry of the <Emphasis Type="Italic">A</Emphasis>1 phase

We solve the Leggett equations for the BCS-BEC crossover in a three dimensional resonance p-wave superfluid with the symmetry of the A1 phase. We calculate the sound velocity, the normal density, and the specific heat for the BCS domain (μ > 0), for the BEC domain (μ < 0), and close to the important point μ = 0 in the 100% polarized case. We find the indications of a quantum phase transition close to the point μ(T = 0) = 0. Deep in the BCS and BEC domains, the crossover ideas of Leggett, Nozieres, and Schmitt-Rink work quite well. We discuss the spectrum of orbital waves, the paradox of intrinsic angular momentum and the complicated problem of chiral anomaly in the BCS A1 phase at T = 0. We present two different approaches to the chiral anomaly, based on supersymmetric hydrodynamics and on the formal analogy with the Dirac equation in quantum electrodynamics. We evaluate the damping of nodal fermions due to different decay processes in the superclean case at T = 0 and find that a ballistic regime ωτ ≫ 1 occurs. We propose to use aerogel or nonmagnetic impurities to reach the hydrodynamic regime ωτ ≪ 1 at T = 0. We discuss the concept of the spectral flow and exact cancelations between time derivatives of anomalous and quasiparticle currents in the equation for the total linear momentum conservation. We propose to derive and solve the kinetic equation for the nodal quasiparticles in both the hydrodynamic and ballistic regimes to demonstrate this cancelation explicitly. We briefly discuss the role of the other residual interactions different from damping and invite experimentalists to measure the spectrum and damping of orbital waves in the A phase of ³He at low temperatures.