arXiv subjects
Publications and source records attributed to J. Dobes.
Reduced probabilities B(E2) of γtransitions between states of positive parity in the ^160Dy nucleus are calculated within the framework of the interacting boson model (IBM-1). The results are compared with the experimental data.
Positive-parity levels and 16 rotational bands are theoretically analyzed on the basis of phenomenological models of the atomic nucleus with the use of new experimental data on excited states in the ^{160}Dy nucleus recently gained in the investigation of the decay ^{160}Er → ^{160m,g}Ho → ^{160}Dy.
The SU(4) algebraic model of high-temperature superconductivity is studied employing the boson mapping techniques. The bosonization of the model enables us to get exact numerical solution of the model. The order parameters are discussed. The situation close to the SO(5) dynamical symmetry limit is interpreted as a modelling case for the behaviour of $D$-wave superconducting and antiferromagnetic phases in cuprates.
Neutron-proton pairing correlations are studied within the context of two solvable models, one based on the algebra SO(5) and the other on the algebra SO(8). Boson-mapping techniques are applied to these models and shown to provide a convenient methodological tool both for solving such problems and for gaining useful insight into general features of pairing. We first focus on the SO(5) model, which involves generalized T=1 pairing. Neither boson mean-field methods nor fermion-pair approximations are able to describe in detail neutron-proton pairing in this model. The analysis suggests, however, that the boson Hamiltonian obtained from a mapping of the fermion Hamiltonian contains a pairing force between bosons, pointing to the importance of boson-boson (or equivalently four-fermion) correlations with isospin T=0 and spin S=0. These correlations are investigated by carrying out a second boson mapping. Closed forms for the fermion wave functions are given in terms of the fermion-pair operators. Similar techniques are applied -- albeit in less detail -- to the SO(8) model, involving a competition between T=1 and T=0 pairing. Conclusions similar to those of the SO(5) analysis are reached regarding the importance of four-particle correlations in systems involving neutron-proton pairing.
Within the context of the isovector-pairing SO(5) model, three methods measuring numbers of different kinds of nucleon pairs are discussed. Though methods do not give the same results, the odd-even staggering in pair numbers in even-even and odd-odd N=Z nuclei and the reduction of the np pair number with increasing T_z is observed in all three procedures.
It is shown how the boson mapping formalism may be applied as a useful many-body tool to solve a fermion problem. This is done in the context of generalized Ginocchio models for which we introduce S-, D-, and G-pairs of fermions and subsequently construct the sdg-boson realizations of the generalized Dyson type. The constructed SO(12) and Sp(10) fermion models are solved beyond the explicit symmetry limits. Phase transitions to rotational structures are obtained, also in situations where there is no underlying SU(3) symmetry.