Gamma-ray transitions in Bi following the decay of Po

The decay of 5.7 h ²⁰⁷Po to levels in ²⁰⁷Bi has been studied using a Ge(Li) detector. Combining the relative gamma-ray intensities with previously established conversion electron intensities, K-conversion coefficients are determined. The multipolarities of 29 transitions are deduced from a comparison with theoretical conversion coefficients, thus establishing the following spins and parities for the excited levels:

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. A comparison with a recent shell-model calculation shows good agreement for all negative parity levels.     

Update on pion weak decay constants in nuclear matter

The QCD sum rule calculation of the in-medium pion decay constants using pseudoscalar–axial-vector correlation function,

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is revisited. In particular, we argue that the dimension 5 condensate, , which is crucial for splitting the time (f_t) and space (f_s) components of the decay constant, is not necessarily restricted to be positive. Its positive value is found to yield a tachyonic pion mass. Using the in-medium pion mass as an input, we fix the dimension 5 condensate to be around −0.025 GeV²−0.019 GeV². The role of the N and Δ intermediate states in the correlation function is also investigated. The N intermediate state is found not to contribute to the sum rules. For the Δ intermediate state, we either treat it as a part of the continuum or propose a way to subtract explicitly from the sum rules. With (and without) explicit Δ subtraction while allowing the in-medium pion mass to vary within 139 MeVm_π^*159 MeV, we obtain f_s/f_π=0.370.78 and f_t/f_π=0.630.79.     

Direct decays of heavy quarkonia

The branching ratios are evaluated of the ψ (3770) and (4S) decays into ππ, , ωπ⁰, ωη, ωη ′, π, η, η′, , . They arise due to the transition through the real intermediate states and , respectively. It is shown that some branching ratios exceed the three-gluon one by an order of magnitude. The rates of the decays ,

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and are evaluated also. τ-C and B factories coul be good tools for studying all decays mentioned.     

Generalized holonomy of supergravities with 8 real supercharges

We show that the generalized holonomy groups of ungauged supergravity theories with 8 real supercharges must be contained in

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, where is the generalized structure group. Here n=4ν is the number of preserved supersymmetries, so the allowed values are limited to n=0,4,8. In particular, solutions of ungauged supergravities in four, five and six dimensions are examined and found to explicitly follow this pattern. We also argue that the G-structure has to be a subgroup of this generalized holonomy group, which may provide a possible classification for supergravity vacua with respect to the number of supercharges.     

The dilambda and the pentaquark in the constituent quark model

We use the non-relativistic constituent quark model and the bag model to study the stability of the dilambda H = (uuddss) and pentaquark states

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. While they are stable in the limit of exact SU(3)_F flavour symmetry between u, d, and s quarks, the H and the P become unbound when a realistic breaking of SU(3)_F is introduced.     

On the normalization of Gamow functions

It is proved that the definitions of the norm given by Berggren and Romo are identical. Regularization in ref. ¹) with any convergence factor of the form

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leads to the same result. The existence of the norm is also established for the proton. The norm for neutrons is analytically given.     

A thermodynamic and electrical conductivity study of nonstoichiometric cerium dioxide

Thermodynamic and dc electrical conductivity measurements were performed on nonstoichiometric CeO_2−x to characterize the electrical behavior and defect structure in the vicinity of the n to p transition. Using the mass action approach, activation energies of 2.57, 1.15 and 0.63 eV were obtained for the electron, hole and ionic partial conductivities respectively (600–1000°C, 1<P_o2<10⁻⁴ atm). Thermodynamic measurements of 99.99%CeO_2-x by electrochemical coulometric titration yielded expressions for point defect concentrations per cm³ and nonstoichiometry in the impurity dominated region at 800°C as follows:

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. Thermodynamic constant composition measurements revealed a decrease in the partial molar enthalpy (from - 10 eV) with decreasing stoichiometry for x<10^−2.8. This decrease is attributed to defect reaction involving both holes and electrons.     

A limit on the lepton-family number violating process π → μe

A FNAL E799 Collaboration has carried out a search for the lepton-family number violating decay π⁰ → μ^±e using π⁰'s produced from K_L → π⁰π⁰π⁰ decays in flight. No events were observed. Assuming that lepton-family number violation is charge independent, the 90% confidence level upper limit on

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was determined to be 8.6 × 10⁻⁹.     

Photinos from gravitational collapse

Very light photinos, if they exist, should be produced in a SN explosion. Using the data from SN 1987A we set limits on the masses of selectrons (and squarks), the SUSY particles involved in the production (and diffusion) of photinos in the stellar medium. The bounds obtained are

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, where .     

Characteristics of heavy ion tracks in bubble detectors

Characteristics of tracks created by heavy ions in bubble detectors have been studied in detail by using four types of super long (23 cm), self-made bubble detectors and six species of high energy heavy ions: ¹²C, ²⁸Si, ⁴⁰Ar, ⁵⁶Fe, ⁸⁴Kr and ¹³²Xe. The following characteristics of heavy ion tracks in bubble detectors have been recognized:

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The first eigenvalue of the Dirac operator on Kähler manifolds

If M^2m is a closed Kähler spin manifold of positive scalar curvature R, then each eigenvalue λ of type r (r {1, …, [(m + 1)/2]}) of the Dirac operator D satisfies the inequality λ² ≥ rR₀/4r − 2, where R₀ is the minimum of R on M^2m. Hence, if the complex dimension m is odd (even) we have the estimation

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for the first eigenvalue of D. In the paper is also considered the limiting case of the given inequalities. In the limiting case with m = 2r − 1 the manifold M^2m must be Einstein. The manifolds S², S² × S², S² × T², P³( ), F( ), P³( ) × T² and F( ³) × T², where F( ³) denotes the flag manifold and T² the 2-dimensional flat torus, are examples for which the first eigenvalue of the Dirac operator realizes the limiting case of the corresponding inequality. In general, if M^2m is an example of odd complex dimension m, then M^2m × T² is an example of even complex dimension m + 1. The limiting case is characterized by the fact that here appear eigenspinors of D² which are Kählerian twistor-spinors.     

Oxygen self-diffusion in single-crystal MgO: secondary-ion mass spectrometric analysis with comparison of results from gas–solid and solid–solid exchange

Self-diffusion coefficients for ¹⁸O in single-crystal MgO have been determined from a novel specimen comprising an epitaxial layer of high-purity Mg¹⁸O upon a single crystal substrate of normal MgO. Heating the specimen in air produced a gas–solid exchange gradient at the sample surface as ¹⁸O in the epitaxial layer exchanged with ¹⁶O in air. A solid–solid interdiffusion gradient was produced between the substrate crystal and the ¹⁸O-enriched epitaxial layer. SIMS analysis of gas–solid exchange gradients prepared in the temperature range 1000–1650 °C provided diffusion coefficients that could be described as

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. Interdiffusion gradients produced by annealing at 1100 and 1200 °C yielded the self-diffusion coefficients that were comparable to those obtained from gas–solid exchange, indicating that the surface exchange reaction is fast enough. The results are interpreted in terms of a defect model in which oxygen diffusion occurs by an interstitial type of defect as a result of suppression of anion vacancy concentration by large concentrations of extrinsic cation vacancies.     

Disorder effects on transport near AFM quantum phase transitions

We discuss three different scenarios recently proposed to account for the non-Fermi liquid behavior near antiferromagnetic (AFM) quantum critical points in heavy-Fermion systems: (i) scattering of Fermi liquid quasiparticles by strong spin fluctuations near the spin-density-wave instability, (ii) the breakdown of the Kondo effect due to the competition with the RKKY interaction, and (iii) the formation of magnetic regions due to rare configurations of the disorder. Here we focus on the first scenario and show that it explains in some detail the anomalous temperature dependence of the resistivity observed, e.g. in CePd₂Si₂, CeNi₂Ge₂ or CeIn₃. The interplay of strongly anisotropic scattering due to critical spin-fluctuations and weak isotropic impurity scattering leads to a regime with a resistivity

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for sufficiently large T and small ρ₀.     

How unitarity imposes a steep small-x rise of spin structure function gLT=g1+g2 and breaking of DIS sum rules

We derive a unitarity relationship between the spin structure function g_LT(x,Q²)=g₁(x,Q²)+g₂(x,Q²), the LT interference diffractive structure function and the spin-flip coupling of the pomeron to nucleons. Our diffractive mechanism gives rise to a dramatic small-x rise

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, where δ_g is an exponent of small-x rise of the unpolarized gluon density in the proton at a moderate hard scale for light flavour contribution and large hard scale for heavy flavour contribution. It invalidates the Burkhardt–Cottingham sum rule. The found small-x rise of diffraction driven g_LT(x,Q²) is steeper than given by the Wandzura–Wilczek relation under conventional assumptions on small-x behaviour of g₁(x,Q²).     

A photoluminescence study of the effects of hydrogen on deep levels in MBE grown GaAlAs:Si

We present a study on low-temperature photoluminescence (PL) of Si-doped

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grown by MBE in the presence and in the absence of a hydrogen backpressure, and post-growth hydrogenated or not, by exposure to a hydrogen plasma. The PL spectra of GaAlAs grown without hydrogen are dominated by transitions involving relatively deep donors and/or acceptors independently on whether the material is post-growth hydrogenated. On the contrary, the spectra of GaAlAs grown in the presence of hydrogen are characterized by recombinations related to excitons and/or to shallow donors and acceptors. Both the in-situ and the ex-situ processes result in PL efficiency enhancements, which are definitely larger (by a factor of up to 20) when the former treatment is used. All of the above results suggest that the ex-situ and the in-situ treatments may affect deep levels of different origin, such as DX centers (related to the band structure of the semiconductor) and levels associated to Al-O complexes, respectively.     

The investigation of compound YAG phase-conjugate resonator

How to improve the quality of output beam of phase-conjugation cavity is a problem. And there are a few reports on how to improve the quality of output beam mode [1]. On this paper, the output characteristic of compound phase-conjugate resonator was reported. The experiment results indicated that it has high output energy and excellent mode. The output energy is 7.4 mJ, and the width of it is about 15 ns. The results of pulse widths and output energies and beam profiles were given and it indicates that using the compound cavity is a useful and easy method to improve the quality of beam mode.     

Studies of the structures formed by the alternated electrodeposition of atomic layers of Cd and Te on the low-index planes of Au: I. LEED and Auger studies

We present here a low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) study of the surface chemistry resulting from electrodeposition of two monolayers of CdTe on the low-index planes of Au by electrochemical atomic layer epitaxy (ECALE). ECALE is the electrochemical analog of atomic layer epitaxy (ALE). In the present study, well-ordered monolayers of CdTe were formed by the alternated electrodeposition of atomic layers of Cd and Te, at underpotential, on all three Au planes. Deposition of the first monolayer of CdTe was performed by depositing Te either oxidatively at underpotential or reductively at underpotential, followed by reductive Cd underpotential deposition (UPD). The structures formed were the same in both cases: Au(100)( , Au(110)(2 × 3)-CdTe, and

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. Varying the initial coverage of Te did not change the resulting CdTe structure, although the higher coverages of Te showed sharper LEED patterns and no emersed oxygen. Deposition of Cd as the first atomic layer followed by oxidative Te UPD resulted in the same structures as those found when Te was used for the first atomic layer. Optimal CdTe monolayers were formed on surfaces where the first atomic layer deposited was homogeneously distributed and of the correct coverage. The correct initial coverage is determined by the coverage needed to complete the subsequently formed CdTe monolayer. On Au(100), an initial coverage of 0.5 appears to be optimal in order to form the Au(100)( . Deposition of a second CdTe monolayer onto the first resulted in structures similar to the first monolayer, but with increased diffuse intensity in the resulting LEED patterns under the conditions used.     

Chiral dynamics and antikaon-nuclear quasibound states

Recent developments are summarised concerning low-energy interactions as they relate to the possible existence of antikaon-nuclear quasibound states. An exploratory study of antikaons bound to finite nuclei is performed, with emphasis on the evolution of such states from light to heavy nuclei (A = 16–208). The energy dependent, driving attractive interactions are constructed using the s-wave coupled-channel amplitudes involving the Λ(1405) and resulting from chiral SU(3) dynamics, plus p-wave amplitudes dominated by the Σ(1385). Effects of Pauli and short-range correlations are discussed. The decay width induced by K⁻NN two-body absorption is estimated and found to be substantial. It is concluded that -nuclear quasibound states can possibly exist with binding energies ranging from 60 to 100 MeV, but with short life times corresponding to decay widths of similar magnitudes.     

Microscopic theory of dissipation for slowly time-dependent mean field potentials

We study the dissipation rate in systems of nucleons bound by a slowly time-dependent mean-field potential and slightly interacting between themselves. Starting from the many-body linear response formula we evaluate an expression for in terms of the pure shell-model quantities and the nucleon–nucleon collision rate Γ. The application of the classical sum rule leads then to an expression for in terms of the classical-path integral with the weighting function including Γ. For vanishing Γ this expression reduces to the Koonin–Randrup Knudsen-gas formula. For simplified Skyrme interactions the classical approximation for the Γ itself is obtained. In leptodermous systems the classical-path expression for decomposes into the wall formula and the multiple-reflection term owing to incomplete randomization of particle motion between consecutive encounters with the boundary. The mean-free path and temperature dependence of dissipation is analyzed for small-amplitude distortions of spherical cavities.