Phase diagram of an extended Agassi model

Background: The Agassi model is an extension of the Lipkin-Meshkov-Glick model that incorporates the pairing interaction. It is a schematic model that describes the interplay between particle-hole and pair correlations. It was proposed in the 1960's by D. Agassi as a model to simulate the properties of the quadrupole plus pairing model. Purpose: The aim of this work is to extend a previous study by Davis and Heiss generalizing the Agassi model and analyze in detail the phase diagram of the model as well as the different regions with coexistence of several phases. Method: We solve the model Hamiltonian through the Hartree-Fock-Bogoliubov (HFB) approximation, introducing two variational parameters that play the role of order parameters. We also compare the HFB calculations with the exact ones. Results: We obtain the phase diagram of the model and classify the order of the different quantum phase transitions appearing in the diagram. The phase diagram presents broad regions where several phases, up to three, coexist. Moreover, there is also a line and a point where four and five phases are degenerated, respectively. Conclusions: The phase diagram of the extended Agassi model presents a rich variety of phases. Phase coexistence is present in extended areas of the parameter space. The model could be an important tool for benchmarking novel many-body approximations.Comment: Accepted for publication in PR

An extended Agassi model: algebraic structure, phase diagram, and large size limit

The Agassi model is a schematic two-level model that involves pairing and monopole-monopole interactions. It is, therefore, an extension of the well known Lipkin-Meshkov-Glick (LMG) model. In this paper we review the algebraic formulation of an extension of the Agassi model as well as its bosonic realization through the Schwinger representation. Moreover, a mean-field approximation for the model is presented and its phase diagram discussed. Finally, a $1/j$ analysis, with $j$ proportional to the degeneracy of each level, is worked out to obtain the thermodynamic limit of the ground state energy and some order parameters from the exact Hamiltonian diagonalization for finite$-j$.Comment: Accepted in Physica Scripta. Focus on SSNET 201

A Symmetry Adapted Approach to Molecular Spectroscopy: The Anharmonic Oscillator Symmetry Model

We apply the Anharmonic Oscillator Symmetry Model to the description of vibrational excitations in ${\cal D}_{3h}$ and ${\cal T}_d$ molecules. A systematic procedure can be used to establish the relation between the algebraic and configuration space formulations, by means of which new interactions are found in the algebraic model, leading to reliable spectroscopic predictions. We illustrate the method for the case of ${\cal D}_{3h}$-triatomic molecules and the ${\cal T}_d$ Be-cluster.Comment: 12 pages, invited talk at XIX Oaxtepec Symposium on Nuclear Physics, January 199

Four-body continuum-discretized coupled-channels calculations using a transformed harmonic oscillator basis

The scattering of a weakly bound three-body system by a target is discussed. A transformed harmonic oscillator basis is used to provide an appropriate discrete and finite basis for treating the continuum part of the spectrum of the projectile. The continuum-discretized coupled channels framework is used for the scattering calculations. The formalism is applied to different reactions, 6He+12C at 229.8 MeV, 6He+64Zn at 10 and 13.6 MeV, and 6He+208Pb at 22 MeV, induced by the Borromean nucleus 6He. Both the Coulomb and nuclear interactions with a target are taken into account.Comment: Published in Phys. Rev.

Excited-state quantum phase transitions in the anharmonic Lipkin-Meshkov-Glick model: Static aspects

The basic Lipkin-Meshkov-Glick model displays a second-order ground-state quantum phase transition and an excited-state quantum phase transition (ESQPT). The inclusion of an anharmonic term in the Hamiltonian implies a second ESQPT of a different nature. We characterize this ESQPT using the mean field limit of the model. The alternative ESQPT, associated with the changes in the boundary of the finite Hilbert space of the system, can be properly described using the order parameter of the ground-state quantum phase transition, the energy gap between adjacent states, the participation ratio, and the quantum fidelity susceptibility.I + D + i Projects - MCIN/AEI PID2019-104002GB-C21 PID2019104002GB-C22 PID2020-114687GB-I00 MCIN/AEI/10.13039/501100011033Junta de AndaluciaEuropean Commission UHU-1262561 US-1380840Junta de Andalucia P20_01247ERDF-A Way of Making Europe European CommissionSpanish Government UNHU-15CE-2848European Union NextGenerationEU/PRT

Recovery and creative practices in people with severe mental illness: evaluating well-being and social inclusion

Purpose: This mixed (quantitative-qualitative) study evaluates the impact of an artistic workshop on a group of people with severe mental illness. This study focuses on the impact of creative practices on well-being and social inclusion outcomes. Method: After participating in a creative workshop, 31 people diagnosed with a severe mental illness completed pre/post-intervention measures, namely, the Warwick-Edinburgh Mental Well-Being Scale and the Social Inclusion questionnaire. It was applied in two-way repeated measures analysis of variance. The statistic Wilcoxon and Kruskal-Wallies were applied for non-parametric data to measure pre/post-test effects and workshop experience effects respectively. In addition to quantitative measures, one observer participated in each workshop that ran in parallel in order to deepen and triangulate quantitative outcomes. Results: The qualitative and quantitative results show that social inclusion improved in a significant way with an important size effect. Psychological wellbeing increased significantly with a low size effect. Conclusions: In accordance with these results, creative practices with people diagnosed with severe mental illness are recommended. In order to increase the impact of these interventions, it is recommended to utilize public space away from clinical environments and to include people without severe mental illness in creative activities together with severe mental illness patients

Biogeographical characterization of Trichodoridae in the Iberian Peninsula

The existence of two faunistic groups has been found on analysis of the distribution patterns of the 18 species from the family Trichodoridae that have been found in representative crops and environments of the Iberian Peninsula. The first one represented by the autochthonous species, Paratrichodorus hispanus, Trichodorus azorensis, T. beirensis, T. giennensis and T. lusitanicus, is present in uncultivated and cultivated areas; T. azorensis, T. beirensis and T. giennensis have been found very localised, while P. hispanus is widespread in Spain and Northern Portugal and T. lusitanicus is common mainly in southern but also found in central Portugal. The second one is defined by the plant parasitic and virus vector species, P. minor, P. pachydermus, P. teres, T. primitivus, T. sparsus and T. viruliferus, in which P. anemones and T. similis could also be included, in spite of their very localised presence. Paratrichodorus anemones, P. pachydermus, T. similis and T. viruliferus could be regarded as characteristic species from temperate environments, while P. minor, the most widespread species in subtropical crops, has also been found in the Canary and Madeira Islands. On the other hand, P. teres, T. giennensis, T. similis, T. sparsus and T. viruliferus have only been found in Spain, while P. acutus, P. allius, P. nanus, P. porosus, T. azorensis and T. orientalis appeared very localised only in Portugal, P. acutus, P. porosus and T. azorensis appearing only in the Azores and Madeira Archipelagos. Climatic, vegetation and soil type influence are discussed.Fundação para a Ciência e a Tecnologia (FCT)CBMA, U

Three-body continuum discretization in a basis of transformed harmonic oscillator states

The inclusion of the continuum in the study of weakly-bound three-body systems is discussed. A transformed harmonic oscillator basis is introduced to provide an appropriate discrete and finite basis for treating the continuum part of the spectrum. As examples of the application of the method the strength functions corresponding to several operators that couple the ground state to the continuum are investigated, for 6He, and compared with previous calculations. It is found that the energy moments of these distributions are accurately reproduced with a small basis set.Comment: 12 figures, submitted to PR