Combining complex and radial slave boson fields within the Kotliar-Ruckenstein representation of correlated impurities

The gauge symmetry group of any slave boson representation allows to gauge away the phase of bosonic fields. One benefit of this radial field formulation is the elimination of spurious Bose condensations when saddle-point approximation is performed. Within the Kotliar-Ruckenstein representation, three of the four bosonic fields can be radial while the last one has to remain complex. In this work, we present the procedure to carry out the functional integration involving constrained fermionic fields, complex bosonic fields, and radial bosonic fields. The correctness of the representation is verified by exactly evaluating the partition function and the Green's function of the Hubbard model in the atomic limit.Comment: 9 pages, 2 figure

Spin and charge modulations of a half-filled extended Hubbard model

We introduce and analyze an extended Hubbard model, in which intersite Coulomb interaction as well as a staggered local potential (SLP) are considered, on the square lattice at half band filling, in the thermodynamic limit. Using both Hartree-Fock approximation and Kotliar and Ruckenstein slave boson formalism, we show that the model harbors charge order (CO) as well as joint spin and charge modulations (SCO) at finite values of the SLP, while the spin density wave (SDW) is stabilized for vanishing SLP, only. We determine their phase boundaries and the variations of the order parameters in dependence on the SLP, as well as on the on-site and nearest-neighbor interactions. Domains of coexistence of CO and SCO phases, suitable for resistive switching experiments, are unraveled. We show that the novel SCO systematically turns into the more conventional SDW phase when the zero-SLP limit is taken. We also discuss the nature of the different phase transitions, both at zero and finite temperature. In the former case, no continuous CO to SDW (or SCO) phase transition occurs. In contrast, a paramagnetic phase (PM), which is accompanied with continuous phase transitions towards both spin or charge ordered phases, sets in at finite temperature. A good quantitative agreement with numerical simulations is demonstrated, and a comparison between the two used approaches is performed.Comment: 17 pages, 7 figure

Informações contábeis e retornos de ações no mercado de ações do Vietnã: abordagem de aprendizado de máquina

This paper studies the relationship between accounting information reflected in financial statements and stock return in Vietnam Stock Market. The authors propose a research model to define the relationship. Besides, machine learning algorithms are used in researching and forecasting, with data obtained from observed firms during the period from 2009 to 2020. Research results show that gradient boosting algorithm has the best self-reporting performance and finan-cial ratios also have great impact on stock returns, including operating income growth, stock earnings volatility, dividend yield, earnings before tax-to-equity ratio, cash holding ratio, and accrual quality. Based on the research results, the authors make some recommendations for investors, firms, and policy makers.Este artículo estudia la relación entre la información contable reflejada en los estados financieros y el rendimiento de las acciones en el mercado de valores de Vietnam. Se propone un modelo de investigación para definir la relación. Además, los algoritmos de aprendizaje automático se utilizan en la investigación y la previsión, con datos obtenidos de empresas observadas durante el período de 2009 a 2020. Los resultados de la investigación muestran que el algoritmo gradient boosting tiene el mejor rendimiento de autoinforme y los índices financieros también tienen un gran impacto en la rentabilidad de las acciones, al incluir el crecimiento de los ingresos operativos, la volatilidad de las ganancias de las acciones, el rendimiento de los dividendos, la relación entre las ganancias antes de impuestos y el capital, la relación de tenencia de efectivo, y la calidad de la acumulación. Sobre la base de los resultados de la investigación, se hacen algunas recomendaciones para inversionistas, empresas y formuladores de políticas.Este artigo estuda a relação entre as informações contábeis refletidas nas demonstrações financeiras e o retorno das ações no mercado de ações do Vietnã. Os autores propõem um modelo de pesquisa para definir a relação. Além disso, algoritmos de aprendizado de máquina são usados em pesquisas e previsões, com dados obtidos de empresas observadas durante o período de 2009 a 2020. Os resultados da pesquisa mostram que o algoritmo gradient boosting tem o melhor desempenho de autorrelato e os índices financeiros também têm grande impacto nos retornos das ações, incluindo crescimento da receita operacional, volatilidade do lucro das ações, rendimento de dividendos, lucro antes do índice de impostos sobre o patrimônio líquido, índice de retenção de caixa e qualidade de acumulação. Com base nos resultados da pesquisa, os autores fazem algumas recomendações para investidores, empresas e formuladores de políticas

Scanning SQUID microscopy of vortex clusters in multiband superconductors

In type-1.5 superconductors, vortices emerge in clusters, which grow in size with increasing magnetic field. These novel vortex clusters and their field dependence are directly visualized by scanning SQUID microscopy at very low vortex densities in MgB2 single crystals. Our observations are elucidated by simulations based on a two-gap Ginzburg-Landau theory in the type-1.5 regime.Comment: 4 pages, 5 figures, to be published in Physical Review

Sub-National Institutions and Firm Survival in Vietnam

By combining two sets of survey data - provincial competitiveness index (PCI) from VNCI-VCCI and USAID and annual enterprise census from Vietnam General Statistics Office (GSO) for the period between 2005 and 2011, we estimate the effects of sub-national institutions measured by Provincial Competitiveness Index on firm survival in Vietnam. Our results show that sub-national institutions have a positive effect on firm’s survival in both short-run and long-run. The effect, however, diminishes over time, indicating that newly entered firms are more likely to survive

Sub-National Institutions and Firm Survival in Vietnam

By combining two sets of survey data - provincial competitiveness index (PCI) from VNCI-VCCI and USAID and annual enterprise census from Vietnam General Statistics Office (GSO) for the period between 2005 and 2011, we estimate the effects of sub-national institutions measured by Provincial Competitiveness Index on firm survival in Vietnam. Our results show that sub-national institutions have a positive effect on firm’s survival in both short-run and long-run. The effect, however, diminishes over time, indicating that newly entered firms are more likely to survive

Le portail g-INFO pour surveiller la grippe Influenza A

Le portail g-INFO pour surveiller la grippe Influenza

On the theory of the vortex state in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase

We demonstrate that the vortex state in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase may be very different depending on the field orientation relative to the crystalline axes. We calculate numerically the upper critical field near the tricritical point taking into account the modulation of the order parameter along the magnetic field as well as the higher Landau levels. For s-wave superconductors with the anisotropy described by an elliptical Fermi surface we propose a general scheme of the analysis of the angular dependence of upper critical field at all temperatures on the basis of the exact solution for the order parameter. Our results show that the transitions (with tilting magnetic field) between different types of mixed states may be a salient feature of the FFLO phase. Moreover we discuss the reasons for the first-order phase transition into the FFLO state in the case of CeCoIn5 compound.Comment: 7 figure