Hesperiidae of Rondônia, Brazil: Porphyrogenes Watson (Lepidoptera: Pyrginae: Eudamini), with descriptions of new species from Central and South America

The pyrgine genus Porphyrogenes Watson, 1893 (Hesperiidae) is discussed, especially as it occurs in central Rondônia, Brazil. Of eleven species of Porphyrogenes found in Rondônia, four (P. specularis, P. convexus, P. sparus, and P. spadix) are described as new species. Biological details of the genus are discussed. An additional five new species of Porphyrogenes (P. spina, P. sporta, P. splendidus, P. simulator, and P. speciosus) are described from elsewhere. Porphyrogenes cervinus (Plötz, 1883), new synonym of Porphyrogenes ferruginea (Plötz, 1883), reinstated status, is raised from a subspecies of Porphyrogenes despecta (Butler, 1870) to species-level. Porphyrogenes omphale (Butler, 1871), reinstated status, is not synonymous with Porphyrogenes passalus (Herrich-Schäffer, 1869) and becomes a species-level taxon for which no subspecies are recognized; P. passalus was described from a female with no known male. Porphyrogenes sula Williams and Bell, 1940, reinstated status, is raised from synonymy with Porphyrogenes zohra (Möschler, 1879) to species-level. Porphyrogenes stresa Evans, 1952, new status, is raised from a subspecies of P. zohra to species-level. Porphyrogenes immaculata (Skinner, 1920), new synonymy, was described from a male, which we believe is the male of Porphyrogenes sororcula (Mabille and Boullet, 1912). Porphyrogenes suva Evans, 1952, new synonymy, formerly considered a full species, was described from a male which we believe is the male of, and thus synonymous with, Porphyrogenes probus (Möschler, 1877). Porphyrogenes virgatus (Mabille, 1888) and Porphyrogenes eudemus (Mabille, 1888), considered synonyms of P. zohra and Porphyrogenes vulpecula (Plötz, 1882), respectively, without justification by Evans (1952), are removed from those synonymies and retained, along with P. passalus, as females without confirmed affinities. Lectotypes are here designated for Phareas ferruginea Plötz, 1883; Augiades despecta Butler, 1870; Telegonus omphale Butler, 1871; Eudamus pausias Hewitson, 1867; Telegonus probus Möschler, 1877; Telemiades vulpecula Plötz, 1882; Eudamus passalus Herrich-Schäffer, 1869; Thymele virgatus Mabille, 1888; and Thymele eudemus Mabille, 1888. A neotype is designated for Phareas cervinus Plötz, 1883, that being the lectotype of Phareas ferruginea. Types of all taxa in the genus are illustrated. Three named and five unnamed phenotypes of females, not reconciled with males, are identified and described. Twenty-six species are now recognized, making this one of the largest hesperiid genera in the neotropics

Flat-band excitonic states in Kagome lattice on semiconductor surface

Excitonic properties in the Kagome lattice system, which is produced by quantum wires on semiconductor surfaces, are investigated by using the exact diagonalization of a tight binding model. It is shown that due to the existence of flat bands the binding energy of exciton becomes remarkably large in the two-dimensional Kagome lattice compared to that in one-dimensional lattice, and the exciton Bohr radius is quite small as large as a lattice constant. We also discuss the magnetic field effects on the exciton binding energy and the stability of exciton against the creation of charged exciton and biexciton.Comment: 5 pages, 5 figure

Ferromagnetism in a Hubbard model for an atomic quantum wire: a realization of flat-band magnetism from even-membered rings

We have examined a Hubbard model on a chain of squares, which was proposed by Yajima et al as a model of an atomic quantum wire As/Si(100), to show that the flat-band ferromagnetism according to a kind of Mielke-Tasaki mechanism should be realized for an appropriate band filling in such a non-frustrated lattice. Reflecting the fact that the flat band is not a bottom one, the ferromagnetism vanishes, rather than intensified, as the Hubbard U is increased. The exact diagonalization method is used to show that the critical value of U is in a realistic range. We also discussed the robustness of the magnetism against the degradation of the flatness of the band.Comment: misleading terms and expressions are corrected, 4 pages, RevTex, 5 figures in Postscript, to be published in Phys. Rev. B (rapid communication

On the chiral anomaly in non-Riemannian spacetimes

The translational Chern-Simons type three-form coframe torsion on a Riemann-Cartan spacetime is related (by differentiation) to the Nieh-Yan four-form. Following Chandia and Zanelli, two spaces with non-trivial translational Chern-Simons forms are discussed. We then demonstrate, firstly within the classical Einstein-Cartan-Dirac theory and secondly in the quantum heat kernel approach to the Dirac operator, how the Nieh-Yan form surfaces in both contexts, in contrast to what has been assumed previously.Comment: 18 pages, RevTe

Generalized Lagrangian of N = 1 supergravity and its canonical constraints with the real Ashtekar variable

We generalize the Lagrangian of N = 1 supergravity (SUGRA) by using an arbitrary parameter $\xi$, which corresponds to the inverse of Barbero's parameter $\beta$. This generalized Lagrangian involves the chiral one as a special case of the value $\xi = \pm i$. We show that the generalized Lagrangian gives the canonical formulation of N = 1 SUGRA with the real Ashtekar variable after the 3+1 decomposition of spacetime. This canonical formulation is also derived from those of the usual N = 1 SUGRA by performing Barbero's type canonical transformation with an arbitrary parameter $\beta (=\xi^{-1})$. We give some comments on the canonical formulation of the theory.Comment: 17 pages, LATE

Relationship between spiral and ferromagnetic states in the Hubbard model in the thermodynamic limit

We explore how the spiral spin(SP) state, a spin singlet known to accompany fully-polarized ferromagnetic (F) states in the Hubbard model, is related with the F state in the thermodynamic limit using the density matrix renormalization group and exact diagonalization. We first obtain an indication that when the F state is the ground state the SP state is also eligible as the ground state in that limit. We then follow the general argument by Koma and Tasaki [J. Stat. Phys. {\bf 76}, 745 (1994)] to find that: (i) The SP state possesses a kind of order parameter. (ii) Although the SP state does not break the SU(2) symmetry in finite systems, it does so in the thermodynamic limit by making a linear combination with other states that are degenerate in that limit. We also calculate the one-particle spectral function and dynamical spin and charge susceptibilities for various 1D finite-size lattices. We find that the excitation spectrum of the SP state and the F state is almost identical. Our present results suggest that the SP and the F states are equivalent in the thermodynamic limit. These properties may be exploited to determine the magnetic phase diagram from finite-size studies.Comment: 17 figures, to be published in Phys. Rev.

Flat-band ferromagnetism induced by off-site repulsions

Density matrix renormalization group method is used to analyze how the nearest-neighbor repulsion V added to the Hubbard model on 1D triangular lattice and a railway trestle (t-t') model will affect the electron-correlation dominated ferromagnetism arising from the interference (frustration). Obtained phase diagram shows that there is a region in smaller-t' side where the critical on-site repulsion above which the system becomes ferromagnetic is reduced when the off-site repulsion is introduced.Comment: 4 pages, RevTex, 6 figures in Postscript, to be published in Phys. Rev.

Flat-Band Ferromagnetism in Organic Polymers Designed by a Computer Simulation

By coupling a first-principles, spin-density functional calculation with an exact diagonalization study of the Hubbard model, we have searched over various functional groups for the best case for the flat-band ferromagnetism proposed by R. Arita et al. [Phys. Rev. Lett. {\bf 88}, 127202 (2002)] in organic polymers of five-membered rings. The original proposal (poly-aminotriazole) has turned out to be the best case among the materials examined, where the reason why this is so is identified here. We have also found that the ferromagnetism, originally proposed for the half-filled flat band, is stable even when the band filling is varied away from the half-filling. All these make the ferromagnetism proposed here more experimentally inviting.Comment: 11 pages, 13figure

Magnetic phase diagram of the Hubbard model with next-nearest-neighbour hopping

We calculate the magnetic phase diagram of the Hubbard model for a Bethe lattice with nearest neighbour (NN) hopping $t_1$ and next nearest neighbour (NNN) hopping $t_2$ in the limit of infinite coordination. We use the amplitude $t_2/t_1$ of the NNN hopping to tune the density of states (DOS) of the non-interacting system from a situation with particle-hole symmetry to an asymmetric one with van-Hove singularities at the lower ($t_2/t_1>0$) respectively upper ($t_2/t_1<0$) band edge for large enough $|t_2/t_1|$. For this strongly asymmetric situation we find rather extended parameter regions with ferromagnetic states and regions with antiferromagnetic states.Comment: 13 pages, 7 figure