4,813 research outputs found
Quaternionic (super)twistors extensions and general superspaces
In a attempt to treat a supergravity as a tensor representation, the
4-dimensional N-extended quaternionic superspaces are constructed from the
(diffeomorphyc)graded extension of the ordinary Penrose-twistor formulation,
performed in a previous work of the authors[14], with N = p + k: These
quaternionic superspaces have 4 + k (N - k) even-quaternionic coordinates and
4N odd- quaternionic coordinates where each coordinate is a quaternion composed
by four C-felds (bosons and fermions respectively). The fields content as the
dimensionality (even and odd sectors) of these superspaces are given and
exemplified by selected physical cases. In this case the number of felds of the
supergravity is determined by the number of components of the tensor
representation of the 4-dimensional N-extended quaternionic superspaces. The
role of tensorial central charges for any N even USp (N) = Sp (N;HC) \ U (N;HC)
is elucidated from this theoretical context.Comment: To be published in the IJGMMP 2016, corrected version, 16 pages
without figure
Quaternionic structures, supertwistors and fundamental superspaces
Superspace is considered as space of parameters of the supercoherent states
defining the basis for oscillator-like unitary irreducible representations of
the generalized superconformal group SU(2m,2n/2N) in the field of quaternions
H. The specific construction contains naturally the supertwistor one of the
previous work by Litov and Pervushin [1] and it is shown that in the case of
extended supersymmetry such an approach leads to the separation of a class of
superspaces and and its groups of motion. We briefly discuss this particular
extension to the domain of quaternionic superspaces as nonlinear realization of
some kind of the affine and the superconformal groups with the final end to
include also the gravitational field[6] (this last possibility to include
gravitation, can be realized on the basis of the reference[12] where the coset
((Sp(8))/(SL(4R)))~((SU(2,2))/(SL(2C)))was used in the non supersymmetric
case). It is shown that this quaternionic construction avoid some
unconsistencies appearing at the level of the generators of the superalgebras
(for specific values of p and q; p+q=N) in the twistor one.Comment: Improved version. Accepted in the International Journal of
Geometrical Methods in Modern Physics (IJGMMP)12 pages, no figures. In
memoriam of Professor Boris Moyseevich Zupnik, pioneer of the development of
supersymmetry, group theory and modern mathematical methods in theoretical
physic
Preliminary analysis of the potential of LANDSAT imagery to study desertification
The use of LANDSAT imagery to define and delimit areas under process of desertification was investigated. Imagery for two different years (1973 and 1978) and two different seasons (dry and rainy seasons in 1976), were used to identify terrain morphology and vegetation cover. The analysis of LANDSAT interpretation, combined with geological and soil information obtained from published literature, allowed the identification of eleven ecological units which were classified corresponding to the degree of the Xique Xique region of Rio Sao Francisco
The use of LANDSAT data to monitor the urban growth of Sao Paulo Metropolitan area
Urban growth from 1977 to 1979 of the region between Billings and the Guarapiranga reservoir was mapped and the problematic urban areas identified using several LANDSAT products. Visual and automatic interpretation techniques were applied to the data. Computer compatible tapes of LANDSAT multispectral scanner data were analyzed through the maximum likelihood Gaussian algorithm. The feasibility of monitoring fast urban growth by remote sensing techniques for efficient urban planning and control is demonstrated
Insulator-metal-insulator transition and selective spectral weight transfer in a disordered strongly correlated system
We investigate the metal insulator transitions at finite temperature for the
Hubbard model with diagonal alloy disorder. We solve the dynamical mean field
theory equations with the non crossing approximation and we use the coherent
potential approximation to handle disorder. The excitation spectrum is given
for various correlation strength and disorder. Two successive metal
insulator transitions are observed at integer filling values as is
increased. An important selective transfer of spectral weight arises upon
doping. The strong influence of the temperature on the low energy dynamics is
studied in details.Comment: submitted to Phys. Rev.
Size-shrinking of deuterons in very dilute superfluid nuclear matter
It is shown within the strong-coupling BCS approach that, starting from the
zero-density limit of superfluid nuclear matter, with increasing density
deuterons first shrink before they start expanding.Comment: 2 pages, Latex, 1 figure included, submitted to Phys. Rev.
Deconfinement phase transition in hybrid neutron stars from the Brueckner theory with three-body forces and a quark model with chiral mass scaling
We study the properties of strange quark matter in equilibrium with normal
nuclear matter. Instead of using the conventional bag model in quark sector, we
achieve the confinement by a density-dependent quark mass derived from
in-medium chiral condensates. In nuclear matter, we adopt the equation of state
from the Brueckner-Bethe-Goldstone approach with three-body forces. It is found
that the mixed phase can occur, for a reasonable confinement parameter, near
the normal nuclear saturation density, and goes over into pure quark matter at
about 5 times the saturation. The onset of mixed and quark phases is compatible
with the observed class of low-mass neutron stars, but it hinders the
occurrence of kaon condensation
Effect of Hund's exchange on the spectral function of a triply orbital degenerate correlated metal
We present an approach based on the dynamical mean field theory which is able
to give the excitation spectrum of a triply degenerate Hubbard model with a
Hund's exchange invariant under spin rotation. The lattice problem can be
mapped onto a local Anderson model containing 64 local eigenstates. This local
problem is solved by a generalized non-crossing approximation. The influence of
Hund's coupling J is examined in detail for metallic states close to the metal
insulator transition. The band-filling is shown to play a crucial role
concerning the effect of J on the low energy dynamics.Comment: Phys. Rev. B (In Press
Equilibrium molecular energies used to obtain molecular dissociation energies and heats of formation within the bond-order correlation approach
Ab initio calculations including electron correlation are still extremely
costly except for the smallest atoms and molecules. Therefore, our purpose in
the present study is to employ a bond-order correlation approach to obtain, via
equilibrium molecular energies, molecular dissociation energies and heats of
formation for some 20 molecules containing C, H, and O atoms, with a maximum
number of electrons around 40. Finally, basis set choice is shown to be
important in the proposed procedure to include electron correlation effects in
determining thermodynamic properties. With the optimum choice of basis set, the
average percentage error for some 20 molecules is approximately 20% for heats
of formation. For molecular dissociation energies the average error is much
smaller: ~0.4.Comment: Mol. Phys., to be publishe
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