Geometric and algebraic descriptions of the 193Ir nucleus

The structure of ¹⁹³Ir was investigated using the ¹⁹¹Ir(2n_th,γ)_and ¹⁹²Os (d,nγ) reactions. High resolution γ and internal conversion spectrometers as well as different Compton-suppressed spectrometers were used. The collective structures are interpreted within the framework of the asymmetric rotor model. The results are also compared to IBFA-1 and IBFA-2 calculations.     

Conversion electron measurements in the124Laβ-decay. Spin and parity assignments in124Ba

Low-lying energy levels in¹²⁴Ba have been investigated from¹²⁴La-decay by using He-jet technique. Spin and parity assignments have been deduced from internal conversion electron measurements. A-vibrational band based on a second 0⁺ state has been identified. Experimental level energies have been compared with IBFA-2 calculations.Deceased in September 1990     

Derivation of the effective pion-nucleon Lagrangian within heavy baryon chiral perturbation theory

We develop a method for constructing the heavy baryon chiral perturbation theory (HBChPT) Lagrangian, to a given chiral order, within HBChPT. We work within SU(2) theory, with only the pion field interacting with the nucleon. The main difficulties, which are solved, are to develop techniques for implementing charge conjugation invariance, and for taking the nucleon on shell, both within the non-relativistic formalism. We obtain complete lists of independent terms in L_HBChPT through O(q³) for off-shell nucleons. Then, eliminating equation-of-motion (e.o.m.) terms at the relativistic and non-relativistic level (both within HBChPT), we obtain L_HBChPT for on-shell nucleons, through O(q³). The extension of the method (to obtain on-shell L_HBChPT within HBChPT) to higher orders is also discussed.     

On the parameters of the minimal supergravity model

We study systematically the interplay of the parameters of the minimalN=1 supergravity model in a large domain of the parameter space. We make use of the renormalization group equations and the requirement of a correct electroweak symmetry breaking. Particular attention is paid to the dependence on the top mass and the ratio of the two vacuum expectation values, tan β=v ₂/v ₁. We also investigate the mass spectrum of the supersymmetric particles within the allowed parameter range and discuss its relevance for LEP.     

Determination of the refractive index over a wide wavelength range through time-delay measurements of femtosecond pulses

We present a simple method to measure the refractive index dispersion over a broad wavelength range (0.6-1.6 μm). In a first step, the optical group indices are obtained by measuring the time-retardation of tunable 150 fs laser pulses within a sample relative to air. The refractive index dispersion is then calculated using a Sellmeier equation that describes the measured group index dispersion. We show that our experimental data agree with previously published results to within 2 × 10⁻⁴ for a 3 mm thick sample of fused silica and to within 3 × 10⁻³ for the index n₁ of a 2 mm thick crystal of the highly dispersive and anisotropic organic crystal 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST).     

Algebraic treatments of the problems of the spin-1/2 particles in the one- and two-dimensional geometry: A systematic study

We consider solutions of the 2 × 2 matrix Hamiltonians of the physical systems within the context of the su (2) and su (1, 1) Lie algebras. Our technique is relatively simple when compared with those of others and treats those Hamiltonians which can be treated in a unified framework of the Sp (4, R) algebra. The systematic study presented here reproduces a number of earlier results in a natural way as well as leads to a novel finding. Possible generalizations of the method are also suggested.     

On the thermodynamic and quantum fluctuations of the cosmological constant

We discuss, from a condensed-matter point of view, the recent idea that the Poisson fluctuations of the cosmological constant about zero could be a source of the observed dark energy [1, 2]. We argue that the thermodynamic fluctuations of Λ are much bigger. Since the amplitude of the fluctuations is ∝ V^?1/2, where V is the volume of the universe, the present constraint on the cosmological constant provides a lower limit for V that is much larger than the volume within the cosmological horizon.     

New form of vector meson dominance and the dependence on the vector meson mass squared

We propose a new form of VMD which relates the reactions πN → VN and γN → πN. Our form fits the experimental results within errors. As our restriction is strong enough, we can discuss the k_μ² dependence. Unexpectedly the k_μ² dependence is larger and this suggest the necessity of generalized vector dominance.     

The electric quadrupole moment of theΩ −

We estimate the electric quadrupole moment of theΩ ^? within current non-relativistic quark models. With only one-gluon exchange as a source of tensor forces we get typically a valueQ _ω=0.004 fm² which is probably very hard to measure experimentally.     

Interacting boson-fermion model of collective states I,the Spin (6) limit

We discuss in detail one of the three possible spinor symmetries of the interacting boson-fermion model. This symmetry, Spin (6), arises when the bosons have SO(6) symmetry and the fermions occupy a single particle orbital with $\text{j =}\text{1}\text{2}$. We derive, within the framework of the Spin (6) symmetry, closed expressions for energies, electromagnetic (EO, M1, E2) transition rates, static moments and (one and two) nucleon transfer reaction intensities.     

Surface induced broadening of the 2p core levels of Al

We observe a drastic broadening of the photoemission lines of the 2p core levels of Al when the surface sensitivity of the measurement is enhanced by an appropriate choice of the photon energy using synchrotron radiation. This surface broadening appears to be quite universal and also occurs for other substances like, e.g. Au. Its possible origin is discussed. There is no surface induced shift of the Al 2p binding energy within ± 40 meV.     

QCD corrections to the Drell-Yan mechanism and the pion structure function

We compute the differential cross section dσ/dQ² dy for lepton pair production up to first order in the strong coupling constant α_s. We show that, in the region where the theory applies and where the statistical accuracy of the experiments is good, the ratio of the QCD correction to the Drell-Yan cross section is approximately constant, and that its magnitude is in good agreement with the results of the CERN-NA3 experiment. We thus show that, within the framework of this first-order calculation, the shape of the pion structure function extracted from dilepton production in πp collisions is approximately correct. We also comment on the average transverse momentum of the dilepton due to gluon or quark recoil.     

A minimal dark matter interpretation for the CRESST-II signal

We report on the possible interpretation of the two proposed dark matter mass values m _?? =11.6 GeV and m _?? =25.3 GeV from CRESST-II within the framework of the Higgs portal minimal dark matter model. We find that the higher mass value yields a suitable fit with a dark matter-Higgs coupling ??/2=0.157 and a recoil cross section which is compatible with contemporary estimates of the effective Higgs?Cnucleon coupling. On the other hand, the lower mass solution would require a large strangeness component in the nucleon to explain the corresponding nucleon recoil cross section reported by CRESST-II.     

On the Q 2 dependence of nuclear structure functions

The recent high statistics NMC data on the Tin to Carbon structure function ratio seems to indicate, for the first time, a significant Q ² dependence, especially at small values of Bjorken x, x < 0.05, and Q ² > 1 GeV². A purely log(Q ²)-type dependence of the structure functions, which is consistent with the free nucleon data, yields a fairly flat ratio with little or no Q ² dependence. In view of this seeming contradiction, we re-examine the applicability of such a model to nuclear structure functions in such a kinematical regime. We find that the model is consistent with all data, within experimental errors, without any need for introducing additional Q ² dependences or higher twist contributions. The model correctly reproduces the Q ² dependence of the Carbon structure function as well. We also critically examine the Q ² dependence of the corresponding spin dependent structure functions.     

Density isomerism and the Primakoff effect

We show that the decay width for π⁰→2γ in nuclear matter could be used as a signal for phase transitions in nuclear matter. The decay width of the π⁰ is experimentally measured using pion photoproduction off heavy nuclei by observing the Primakoff peak in the differential cross sections. We present calculations for the differential cross section with corrections to the γ?γ?π⁰ vertex arising from the nuclear medium within the nuclear radius when the medium is in the abnormal matter phase.     

A precision determination of the radial charge parameters and the quadrupole moment of 181Ta using muonic X-rays

We report the measurement of the energies of the 4f → 3d, 3d → 2p and 2p → 1s atomic transitions in muonic ¹⁸¹Ta. Using transitions to and from the 1s and 2p levels, as well as the hyperfine splittings of the 2p and 3d states, we obtained the radial charge parameters assuming deformed Fermi distributions. We found the intrinsic static quadrupole moment Q₀ = 6.82 ± 0.06 e · b, in excellent agreement with Coulomb excitation results. We verified that the dynamic (corresponding to transitions to the first excited state) and the static (ground state) E2 moments were equal to within 1.1 %. The intrinsic hexadecapole moment was determined to be Π₀ = ?0.12 ± 0.40 e · b².     

Ground state of the SU(2) Yang-Mills theory

The problem of the ground state of the SU(2) Yang-Mills theory is investigated within the one-loop approximation. It is shown that an assumed initial constant magnetic field will be diminished to realize a state of lower energy (vacuumI) by a condensation of some components of Yang-Mill fields. We also find a Lorentz invariant state (vaccumII) through a singlet scalar condensation. However, the vaccumI which is Lorentz noinvariant is found to have a lower energy density than the vacuumII.     

Volume collapse in the Kondo lattice

The α-γ transition of Ce and its compounds are explained within a compressible Kondo lattice model where the variation of |J|/D with volume is taken into account. We show that, contrary to the valence change model, the Kondo contribution is sufficient to induce a first order transition at low temperature from a magnetic to a Kondo phase. The disappearance of magnetism is then related to an extremely high Kondo temperature. Applications to Ce and CeAl₂ cases are given.