An energy-momentum tensor in gauge theories

We consider the renormalization of the twist two, dimension four gauge invariant operator O_μν⁽¹⁾ = − F_μσF_νσ − g_{μν 0}. By using the general theory of renormalization of gauge invariant operators, we find the gauge noninvariant operator O⁽²⁾ with which it mixes. We construct a finite combination of O⁽¹⁾ and O⁽²⁾ and show that it is an acceptable energy momentum tensor for gauge theories. We compare our energy momentum tensor with that constructed by Freedman, Muzinich, and Weinberg.     

Line Parameters for Ozone Hot Bands in the 3.3-μm Spectral Region

Line positions, intensities, and lower state energies have been calculated for eight hot bands of ¹⁶O₃ in the 3.3-μm spectral region. The results are based on spectroscopic parameters deduced in recent high-resolution laboratory studies and improved rotational energy levels of the (103), (004), and (310) vibrational states derived by refitting earlier data and experimental (004) energy levels from measurements of the 4ν₃ - ν₃ hot band. The good quality of the new parameters has been verified through comparisons of line-by-line simulations with high-resolution laboratory spectra. The present work and the results of our analyses of the main bands at 3.6 μm [Smith et al., J. Mol. Spectrosc.139, 171-181 (1990)] and 3.3 μm [Camy-Peyret et al., J. Mol. Spectrosc.141, 134-144 (1990)] provide a complete set of ozone spectroscopic line parameters covering the 3-μm region.     

Magnetic responses in 1D mesoscopic rings and cylinders

I investigated a detailed study of persistent current and low-field magnetic susceptibility in one-dimensional mesoscopic rings and cylinders threaded by slowly varying magnetic flux φ in the tight-binding model. In perfect rings described by constant number of electrons N_e, current shows only saw-tooth variation with φ, while for those rings described by constant chemical potential μ, current varies saw-tooth like for some special choices of μ, but in all other cases it shows kink-like structures. On the other hand, in perfect cylinders I get both saw-tooth and kink-like structures in persistent current whether these cylinders are described by constant N_e or μ. In presence of impurity, current gets a continuous variation with φ only for the rings described by constant N_e, while in all other cases it depends on the choice of μ. My exact calculation predicts that the diamagnetic and paramagnetic sign of the low-field currents can be determined exactly for the rings described by constant N_e. In perfect rings, I get only diamagnetic currents both for odd and even N_e, while in presence of impurity current always shows diamagnetic sign for the rings with odd N_e and paramagnetic sign for the rings with even N_e. Both for the perfect and disordered rings described by constant μ the sign of the current cannot be mentioned exactly since it depends on the choice of μ and disordered configurations. Similar arguments are also true for the cylinders those are described either by constant N_e or by constant μ since the sign of the current in these systems depends on N_e, μ and disordered configurations.     

The Electric Dipole Moment of the CO2–CO van der Waals Complex

Radiofrequency transitions withinK= 2 asymmetry doublets have been observed for the CO₂–CO van der Waals complex. A Stark effect measurement on theJ= 2,K= 2 transition provides an electric dipole moment of μ = 0.2493(1) D. Combining this result with the permanent moment of CO, μ_CO= 0.1098 D, gives a change of moment on complex formation of Δμ = 0.140 D. The sign of Δμ is such that the CO end of the complex is more positive than CO₂. The origin of Δμ should not be attributed to any single mechanism, and several different contributions to Δμ are discussed.     

Three-dimensional stationary cyclic symmetric Einstein–Maxwell solutions; black holes

From a general metric for stationary cyclic symmetric gravitational fields coupled to Maxwell electromagnetic fields within the (2 + 1)-dimensional gravity the uniqueness of wide families of exact solutions is established. Among them, all uniform electromagnetic solutions possessing electromagnetic fields with vanishing covariant derivatives, all fields having constant electromagnetic invariants F_μνF^μν and T_μνT^μν, the whole classes of hybrid electromagnetic solutions, and also wide classes of stationary solutions are derived for a third-order nonlinear key equation. Certain of these families can be thought of as black hole solutions. For the most general set of Einstein–Maxwell equations, reducible to three nonlinear equations for the three unknown functions, two new classes of solutions – having anti-de Sitter spinning metric limit – are derived. The relationship of various families with those reported by different authors’ solutions has been established. Among the classes of solutions with cosmological constant a relevant place is occupied by the electrostatic and magnetostatic Peldan solutions, the stationary uniform and spinning Clement classes, the constant electromagnetic invariant branches with the particular Kamata–Koikawa solution, the hybrid cyclic symmetric stationary black hole fields, and the non-less important solutions generated via SL(2,R)-transformations where the Clement spinning charged solution, the Martinez–Teitelboim–Zanelli black hole solution, and Dias–Lemos metric merit mention.     

Dynamical mechanism for varying light velocity as a solution to cosmological problems

A dynamical model for varying light velocity in cosmology is developed, based on the idea that there are two metrics in spacetime. One metric g_μν describes the standard gravitational vacuum, and the other describes the geometry through which matter fields propagate. Matter propagating causally with respect to can provide acausal contributions to the matter stress-energy tensor in the field equations for g_μν, which, as we explicitly demonstrate with perfect fluid and scalar field matter models, provides a mechanism for the solution of the horizon, flatness and magnetic monopole problems in an FRW universe. The field equations also provide a ‘graceful exit' to the inflationary epoch since below an energy scale (related to the mass of ψ_μ) we recover exactly the standard FRW field equations.     

Families of commuting transfer matrices and integrable models with disorder

A family of commuting transfer matrices is shown to be associated to each symmetry transformation of a given Yang-Baxter algebra. This applies in lattices models and field theory.The Yang-Baxter algebra remains unchanged when an arbitrary parameter μ_l is associated to each lattice site. We generate in this way integrable one-dimensional hamiltonians with long-range couplings and disorder given by the <{;μ₁<};. These operators are lattice versions of the non-local charges in sigma models. As a simple example we get a Dzialozhinski-Moriya interaction with an arbitrary coupling per site from the six-vertex model. A similar model with a disordered magnetic field follows too. Their exact solution by an algebraic Bethe ansatz is presented. We derive the excitations spectrum in terms of the density of parameters (μ).As another application, the total spin S² is computed for a XXZ Heisenberg chain (μ_l ≡ 0) as a function of the anisotropy Δ (− ∞ < Δ < + ∞).     

Enhancement of the Debye frequency due to a charged-boson exchange model of high temperature superconductors

A simple model of 1-2-3 superconductors in which electrons (holes) in CuO₂ planes interact via exchange with two kinds of bosons is considered. Namely, via one-phonon exchange (weak coupling-Cooper pairing), and via paired holes on oxygen O⁰ from Cu-O chains. The mechanisms of paired holes exchange (“charged bosons”-“O⁰” exchange) considered here in strong coupling leads to the enhancement of the Fröhlich constant g_f (g²_F→Kg²F), and as a consequence to the enhancement of the Debye frequency ω_D^K=f^Kω_D, f^K 1. In the proposed model the exact expression for the constant K is derived.     

Status of the CHORUS neutrino oscillation experiment

The CHORUS experiment is designed to search for ν_μ → ν_τ oscillation with a hybrid detector system containing 800 kg nuclear emulsions as target and vertex detector. Run I (320 000 recorded ν_μCC in 1994/5) and more than half of the run II (460 000 ν_μCC in 1996/7) data taking have been successfully completed. Approximately 80 000 events have been analyzed so far, searching for and τ⁻ → h⁻ (nπ⁰) ν_τ decays. No candidate has been found, leading to a limit sin² 2θ_μτ ≤ 4.5 10⁻³ for large Δm².     

Atmospheric neutrinos in the Soudan-2 and MACRO experiments

The results of Soudan-2 and MACRO experiments are summarized. Both experiments observe atmospheric neutrino anomalies in agreement with ν_μ → ν_τ oscillations with maximum mixing. The ν_μ → ν_s oscillations are disfavoured by the MACRO experiment at 98% C.L.     

Quantum–Chemical Investigation of the Influence of Conformations and Extra–Ligation on Electronic Spectra of Chemical Dimers of Metalloporphyrins and Metallochlorins

We have made a theoretical analysis of the factors influencing the electronic absorption spectra of monomers of porphyrins and chlorins as well as of their chemically bound dimers in which the monomeric subunits are bound through the CH₂–CH₂ group. On the basis of quantum–chemical calculations by the semiempirical method CNDO/S it is shown that the addition of extra–ligands causes a change in the conformation of the dimers.     

About the symmetries of the rotation-vibration wavefunction of molecules

The importance recently given to the 3.39 μm methane line, on account of its near-coincidence with a helium-neon laser line, has drawn attention to a discrepancy between different symmetry notations for the vibration-rotation levels of tetrahedral molecules: this line has been denoted F₁ or F₂, depending on the author. The purpose of this note is to point out that either notation may be used, but that it is necessary in all theories to employ some trick to avoid the use of translational wavefunctions. First, I shall make some general comments on the use of group theory.     

Separation of the ortho and para NMR signals in solid deuterium via DQ filtering

Double quantum (DQ) filtering is shown to lead to an effective separation of the NMR signals from the para (I = 1) and ortho (I = 2) molecules in solid deuterium. The separation is achieved by the pulse sequence 90_φ^°–t_pr–90_φ^°–t_ev–90_x^°–t, where the phase-cycled first two pulses create the DQ coherence. Two components are observed after the third pulse; the para signal shows the maximum at a short time t while the ortho signal reaches the maximum at a longer t. The observed signal can be expressed as ∑_I [F_I(t_pr − t) − F_I(t_pr + t)], where F_I(t) is a proper fitting function for the free induction signal of the para and ortho molecules (with I = 1 or 2, respectively). Numerical fits to experimental data at 4.2 and 2 K show that this method can be used to determine the ratio F₁(0)/F₂(0) and thus, because the initial value F_I(0) is proportional to the respective magnetization before the pulse sequence, the ortho and para concentrations in solid deuterium.     

Noncommutative theories, the axial anomaly, Fujikawa's method and the Atiyah–Singer index

Fujikawa's method is employed to compute at first order in the noncommutative parameter the U(1)_A anomaly for noncommutative SU(N). We consider the most general Seiberg–Witten map which commutes with hermiticity and complex conjugation and a noncommutative matrix parameter, θ^μν, which is of “magnetic” type. Our results for SU(N) can be readily generalized to cover the case of general nonsemisimple gauge groups when the symmetric Seiberg–Witten map is used. Connection with the Atiyah–Singer index theorem is also made.     

KARMEN: Neutrino oscillation limits and new results with the upgrade

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS which provides ν_μ's, ν_e's and from the π⁺−μ⁺-decay at rest. The oscillation channels ν_{μ → νe} and are investigated with a 56 t liquid scintillation calorimeter. No evidence for oscillations could be found with KARMEN, resulting in 90% CL exclusion limits of sin²(2Θ) < 8.5 · 10⁻³ ( ) and sin²(2Θ) < 4.0 · 10⁻² (ν_μ → ν_e) for Δm² > 100 eV². In 1996, the experiment has been upgraded by an additional veto counting system with a total coverage of 300 m². The new system allows the identification of cosmic muons in the vicinity of the detector. Vetoing these muons suppresses energetic neutrons from deep inelastic scattering of muons as well as from μ-capture by a factor of 40. Up to 1996, these neutrons represented the main background for oscillation search. The experimental sensitivity for will be significantly enhanced towards sin²(2Θ) 1.0 · 10⁻³ after a further measuring period of 2–3 years.     

In-plane gate transistors in AlxGa1−xN/GaN heterostructures written by focused ion beams

Focused ion beam implantation of gallium and dysprosium was used to locally insulate the near-surface two-dimensional electron gas of Al_xGa_1−xN/GaN heterostructures. The threshold dose for insulation was determined to be 2×10¹⁰ cm⁻¹ for 90 keV Ga⁺ and 1×10⁹ cm⁻¹ for 200 keV Dy²⁺ at 4.2 K. This offers a tool not only for inter-device insulation but also for direct device fabrication. Making use of “open-T” like insulating line patterns, in-plane gate transistors have been fabricated by focused ion beam implantation. An exemplar with a geometrical channel width of 1.5 μm shows a conductance of 32 μS at 0 V gate voltage and a transconductance of around 4 μS, which is only slightly dependent on the gate voltage.     

Lüscher's μ-term and finite volume bootstrap principle for scattering states and form factors

We study the leading order finite size correction (Lüscher's μ-term) associated to moving one-particle states, arbitrary scattering states and finite volume form factors in (1+1)-dimensional integrable models. Our method is based on the idea that the μ-term is intimately connected to the inner structure of the particles, i.e., their composition under the bootstrap program. We use an appropriate analytic continuation of the Bethe–Yang equations to quantize bound states in finite volume and obtain the leading μ-term (associated to symmetric particle fusions) by calculating the deviations from the predictions of the ordinary Bethe–Yang quantization. Our results are compared to numerical data of the E₈ scattering theory obtained by truncated fermionic space approach. As a by-product it is shown that the bound state quantization does not only yield the correct μ-term, but also provides the sum over a subset of higher order corrections as well.     

Soft photon problem in leptonic B-decays

We point out at the peculiarity of B→μν_μ decay, namely the enhancement of the soft photon events which originate from the structure dependent part of the B→μν_μγ amplitude. This may be a dominant source of systematic uncertainty and compromise the projected experimental uncertainty on Γ(B→μν_μ). We show that the effect of these soft photons can be controlled if the experimental cut on identification of soft photons is lowered and especially if the better resolution in identifying the momentum of muon emerging from B→μν_μ is made. A lattice QCD computation of the relevant form factors would be highly helpful for a better numerical control over the structure dependent soft photon emission.     

Experimental measurements of atmospheric neutrinos

This talk reports the latest indications of an anomaly in the measurements of atmospheric neutrinos. New results from Soudan-2 and Super-Kamiokande provide evidence that the ratio of ν_μ to ν_e interactions is not as expected. High energy Super-Kamiokande data indicates the cause is a deficit of upward-going ν_μ, and the zenith angle dependence of the effect is consistent with neutrino oscillations. Upward-going muon measurements by several detectors are discussed, but in total they provide inconclusive evidence for the anomaly.     

Zero Temperature Limits of Gibbs-Equilibrium States for Countable Alphabet Subshifts of Finite Type

Let Σ_A be a finitely primitive subshift of finite type on a countable alphabet. For appropriate functions f:Σ_A → IR, the family of Gibbs-equilibrium states (μ_tf)_t⩾1 for the functions tf is shown to be tight. Any weak^*-accumulation point as t→∞ is shown to be a maximizing measure for f.