Terms Of Quasiparticle Excitations Research Articles

Analytic Flow Equations for the Fermi Liquid Parameters of the Anderson Impurity Model.

The low temperature behavior of a Fermi liquid can be described in terms of quasiparticle excitations that are in 1-1 correspondence with those of the noninteracting system. Because of adiabatic continuity, the Landau parameters, which describe the interactions between the quasiparticles, must evolve continuously as the interactions are turned on and be described by a set of flow equations. For strongly correlated electron systems it is not possible to follow this flow in perturbation theory when the interactions become strong. We explore the idea here of overcoming this problem by renormalizing the quasiparticles in this flow using a renormalized perturbation theory. This approach is tested in the case of a single impurity Anderson model. Analytic flow equations are derived which give excellent results for the Landau parameters in the strong correlation regime.

Shear and bulk viscosities of the gluon plasma in a quasiparticle description

Shear and bulk viscosities of deconfined gluonic matter are investigated within an effective kinetic theory by describing the strongly interacting medium phenomenologically in terms of quasiparticle excitations with medium-dependent self-energies. We show that the resulting transport coefficients reproduce the parametric dependencies on temperature and coupling obtained in perturbative QCD at large temperatures and small running coupling. The extrapolation into the nonperturbative regime results in a decreasing specific shear viscosity with decreasing temperature, exhibiting a minimum in the vicinity of the deconfinement transition, while the specific bulk viscosity is sizable in this region, falling off rapidly with increasing temperature. The temperature dependence of specific shear and bulk viscosities found within this quasiparticle description of the pure gluon plasma is in agreement with available lattice QCD results.

Probing the limits of complete spectroscopy in 164Yb

Abstract High spin states of 164Yb have been populated using the 152Sm(16O,4n) reaction. Analysis has been made using γγ coincidences and, for the first time in a large detector array, angular correlations. The experimental level scheme has been extended to include a total of 15 decay cascades, for some of which the spins have been measured. Extensive cranked shell model calculations have been performed to map the quasiparticle rotational bands in a window, reaching up to 1 MeV above the yrast line, in the spin-energy plane. The experimental data are compared with the calculated bands, and most of the experimental bands are interpreted in terms of quasiparticle excitations. It is also found that the number of experimentally detected bands is in good agreement with the calculated number of bands in the observed spin-energy region.

High spin band structures in104Cd

High spin states in104Cd have been investigated by means of heavy ion induced reactions using the Nordball detector array. The level scheme constructed from γγ-coincidences is dominated by three band structures. The positive parity band shows no rotational like energy spacing. It is thus understood mostly in terms of quasiparticle excitations with vd5/2, vg7/2 andπg9/2 configurations. The collective properties of the negative parity bands are more pronounced. These bands are most likely due to v(h11/2,d5/2) and v(h11/2,g7/2) structures.

High-spin gamma -ray spectroscopy of 165W and 166W

High-spin states of 165W and 166W were studied using the 106Pd(63Cu, p3n) and 106Pd(63Cu, p2n) reactions, respectively. Gamma rays in 165W were identified for the first time using the gamma -ray detector array POLYTESSA and the Daresbury recoil separator. Level schemes for 165W and 166W were constructed from the gamma - gamma coincidence data and angular correlation data from the POLYTESSA and TESSA3 arrays. In 166W the yrast band is established up to 30+ (32+), as well as two side bands up to 22- (28-) and 23- (29-). In 165W the yrast band is established up to 45/2+ and two side bands up to 55/2- (59/2-) and 53/2-. The rotational structures and band crossings observed are interpreted within the framework of the cranked shell model in terms of quasiparticle excitations. The systematics of the second i13/2 neutron alignment in the N=91 and 92 isotones are discussed.

Rotational band structures in 154Gd

The N=90 rare earth nucleus 154Gd has been studied in the spin regime of I<or=26h(cross) by using the reaction 150Nd(9Be, 5n)154Gd at 55 MeV. Gamma-gamma coincidence and angular correlation data were obtained using the TESSA2 array. Two positive parity sequences have been extended to 26+ and four negative parity structures have each been observed up to spins of I=22-24h(cross). The rotational structures observed in 154Gd are interpreted within the framework of the cranked shell model (CSM) in terms of quasiparticle excitations. The characteristics of the rotational band sequences and the band crossings that occur are compared with those in neighbouring nuclei and to the predictions of this model. The first, second and third i13/2 neutron alignments in 154Gd and the systematics of the neutron alignments in the negative parity rotational bands in the even-even N=90 nuclei are discussed. Evidence for quasiproton excitations at the highest spins is discussed.