A coriolis-like effect of the dynamical boson-fermion interaction in the interacting boson-fermion model

It is shown that in a particular basis the dynamical interaction of IBFM for a boson core coupled to a single-j particle in the SU(3) limit takes a tridiagonal form, as does the Coriolis interaction. Interference between this Coriolis-like effect in the boson-fermion dynamical interaction and the genuine Coriolis effect results in interesting features of IBFM: For a particular ratio of the interaction strengths, depending only on the angular momentum of the odd particle, the K = j band exactly follows the rotational energy rule, is completely uncoupled from the other bands and has exactly the same moment of inertia as a ground-state band of the core. A possible interpretation of this feature in terms of spectrum-generating supersymmetry is suggested.     

On the boson-fermion model of superconductivity

Summary The existence of pair excitations in a Fermi gas interacting via a short-range attractive potential is investigated. Within the ladder approximation to the Bethe-Salpeter equation for the effective two-particle interaction, evidence of pair excitation is found at energies slightly larger than the chemical potential. The link between those excitations and a boson-fermion model of superconductivity (Phys. Lett. A,196 (1995) 359) is discussed. In particular it is shown that the charge carrier density dependence of the pair excitation (boson) energy, assumed phenomenologically in the boson-fermion model, is consistent with the properties of the interacting Fermi gas studied. These results give support to the microscopic origin of the phenomenological boson-fermion model of superconductivity. Within the polaron-bipolaron theory the assumption that bosons and fermions can be described as mobile particles has found support in ref.[6] where the small bipolaron (boson) delocalization is discussed and in ref.[7] where the large polaron delocalization is analysed.     

The promethium isotopes in the interacting boson-fermion model

We present a calculation of excitation energies, electromagnetic moments and transition rates and single-particle transfer amplitudes for the odd-mass promethium isotopes in terms of the interacting boson-fermion model. Model parameters are compared with those obtained for the neighbouring europium isotopes.     

Non-degenerate single-particle energies in the Ginocchio model

A one-body operator expressing the breaking of the degeneracy of the single-nucleon energies is added to the pairing interaction of the Ginocchio model. This operator couples states inside the model's SD space to states outside it. The influence of this coupling on the effective interaction in the SD space and the possibility of expressing the results in terms of renormalization of parameters in the fermion hamiltonian or the IBM are investigated. The effective interaction is found to be almost diagonal in seniority, while splitting the previously-degenerate seniority multiplets. Appropriately renormalized Ginocchio and IBM hamiltonians can approximately reproduce the results, but fermion-number dependence of the hamiltonian parameters and explicit three-body interactions are needed to reproduce the computed effects exactly.     

Mean single-particle potentials and single-particle energies in a microscopic model of the nucleus

A method for calculating mean single-particle potentials and the corresponding single-particle energy levels in nuclei is presented. Specific formulas for these quantities are written for Slater determinant wave functions in the case of polarized orbitals and a central exchange nucleon-nucleon potential featuring a Gaussian radial dependence. The resulting theoretical estimates of single-particle properties of the nuclei considered in the present study are in satisfactory agreement with relevant experimental data.     

Nuclear structure of97Y in the interacting boson-fermion model

Unique-parity states of⁹⁷Y are studied in the framework of the interacting boson-fermion model (IBFM). Spin assignments for the levels of the unique-parity yrast band are proposed on the basis of nuclear systematics and the IBFM band pattern associated with coupling of a particle-type quasiparticle (g_9/2) to the SU(5) core₃₈ ⁹⁶Sr₅₈. The good fit of the experimental data with the IBFM calculations confirms the single particle character of this immediate neighbour of the doubly sub-magic nucleus⁹⁶Zr.     

Interacting boson-fermion model analysis for159Tb

The result of an IBFM multilevel calculation with the 3s _1/2, 2d _3/2, 2d _5/2 and 1g _7/2 single particle orbits are reported for the first time for the positive parity states of the odd mass nucleus¹⁵⁹Tb. Comparisons are made with experimental data for energy spectra, transition probabilities, mixing ratios, electric quadrupole and magnetic dipole moments. The agreement with the low-lying spectra suggests an extended comparison up to levels with spin 25/2, thereby testing the predictive power of the model.We would like to thank Dr. D. Mac Mahon and the staff at the Imperial College Reactor Centre for their help and use of facilities. We would also like to thank Dr. P. Van Isacker for many illuminating discussions.     

Multilevel description of the Rh isotopes in the interacting boson-fermion model

We present a multilevel calculation within the framework of the interacting boson-fermion model (IBFM-1) of the odd-mass ^101–109Rh isotopes. We calculate both positive- and negative-parity states of the same hamiltonian, starting from the $\text{1g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$, $\text{2p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, $\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, $\text{lf}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ and $\text{2d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ single-particle orbitals. We discuss energy spectra, electromagnetic E2 transition rates and one-nucleon transfer properties. We also discuss the influence of the $\text{1f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ orbital on the one-nucleon transfer properties. The results of the calculation for the negative-parity states are compared with the results of the $\text{U(}\text{6}\text{12}$) supersymmetry scheme of the interacting boson model.     

Merging of single-particle levels in finite Fermi systems

Properties of the distribution of single-particle levels adjacent to the Fermi surface in finite Fermi systems are studied, focusing on the case in which these levels are degenerate. The interaction of the quasiparticles occupying these levels lifts the degeneracy and affects the distance between the closest levels on opposite sides of the Fermi surface, as the number of particles in the system is varied. In addition to the familiar scenario of level crossing, a new phenomenon is uncovered, in which the merging of single-particle levels results in the disappearance of well-defined single-particle excitations. Implications of this finding are discussed for nuclear, solid-state, and atomic systems. The text was submitted by the authors in English.     

Negative-parity states of75As and the interacting boson-fermion model

The result of an IBFM multilevel calculation with the 2p_3/2, 1f_5/2 and 2p_1/2 single particle orbits is reported for the negative parity states of the odd mass nucleus⁷⁵As. Comparisons are made with experimental data for energy spectra, transition probabilities, mixing ratios, electric quadrupole and magnetic dipole moments. Also, an IBM-1 calculation is presented for the low-lying states in the even-even⁷⁴Ge core nucleus.     

Signature dependence of electromagnetic transitions and the interacting boson-fermion model

The signature dependence of electromagnetic transitions in odd-A nuclei is studied in the interacting boson-fermion model. Three cases are investigated corresponding to the three limits of the interacting-boson-model core. We present various signature-dependent zig-zag patterns as a function of spin in the transition matrix elements. It is shown that the exchange interaction plays a crucial role in determing the signature dependence.     

The self-consistent single-particle model in nuclear physics

The nuclear many body problem is treated in the single particle approximation, i.e. on the basis of the Hartree-Fock-Bogolyubov approximation. Results of various applications are presented and discussed with emphasis on properties of rotational states of deformed nuclei.     

The experimental structure of199Au and the interacting boson-fermion model

Gamma rays of¹⁹⁹Au obtained after double neutron capture in¹⁹⁷Au were measured at the ILL high flux reactor. A level scheme up to 1770 keV excitation energy is established. The result is compared with IBFM and Boson-Fermion-Symmetry calculations.     

High-energy kink in the single-particle spectra of the two-dimensional hubbard model

Employing dynamical cluster quantum Monte Carlo calculations we show that the single-particle spectral weight A(k,omega) of the one-band two-dimensional Hubbard model displays a high-energy kink in the quasiparticle dispersion followed by a steep dispersion of a broad peak similar to recent angle-resolved photoemission spectroscopy results reported for the cuprates. Based on the agreement between the Monte Carlo results and a simple calculation which couples the quasiparticle to spin fluctuations, we conclude that the kink and the broad spectral feature in the Hubbard model spectra is due to scattering with damped high-energy spin fluctuations.     

Collective octupole vibration and proton single-particle levels in zirconium nuclei

Self-energy correction to the shell model single-particle motion, arising from the excitation of octupole vibration in the intermediate state, accounts quite well for the energy shifts of the 2p _1/2 and 1g _9/2 proton orbits in zirconium nuclei.     

The statistical properties of single-particle levels in rotating heavy nuclei

The single particle-energy levels of U ₉₂ ²³⁸ as a function of cranked frequency are given in rotating two-centre shell model. It is found that the curvature distribution approaches the prediction of Gaussian unitary ensemble (GUE) [14] for a certain range of separations between two centers at some cranked frequencies, which is the first support to the prediction in the realistic and complex system like heavy nuclei. Meanwhile, we find that the spacing distributions for various separations have a similar structure when the frequency is high, for which a formulae is suggested to describe this kind of spacing distributions. In addition, we compute the spectral rigidity characterizing the long range correlation of a spectrum.     

Superconducting order in low-dimensional boson-fermion model: absence of finite-temperature transition

We present the application of the McBryan and Spencer method to a model describing a mixture of hard-core bosons and fermions interacting each others via a hybridization coupling. We prove upper bounds for some correlation functions at finite temperature and then rule out the possibility of long-range order of superconducting type in one and two dimensions. Received 21 August 2002 Published online 19 November 2002