15,406 research outputs found
Lattice calculations on the spectrum of Dirac and Dirac-K\"ahler operators
We present a matrix technique to obtain the spectrum and the analytical index
of some elliptic operators defined on compact Riemannian manifolds. The method
uses matrix representations of the derivative which yield exact values for the
derivative of a trigonometric polynomial. These matrices can be used to find
the exact spectrum of an elliptic operator in particular cases and in general,
to give insight into the properties of the solution of the spectral problem. As
examples, the analytical index and the eigenvalues of the Dirac operator on the
torus and on the sphere are obtained and as an application of this technique,
the spectrum of the Dirac-Kahler operator on the sphere is explored.Comment: 11 page
Free fermionic propagators on a lattice
A method used recently to obtain a formalism for classical fields with
non-local actions preserving chiral symmetry and uniqueness of fermion fields
yields a discrete version of Huygens' principle with free discrete propagators
that recover their continuum forms in certain limit.Comment: LaTex document, 13 pages, 1 figure. Minor changes, two references
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MASS SEGREGATION IN DARK MATTER MODELS.
We use the moments of counts of neighbors as given by the Generalized
Correlation Integrals, to study the clustering properties of Dark Matter Halos
(DH) in Cold Dark Matter (CDM) and Cold+Hot Dark Matter (CHDM) models. We
compare the results with those found in the CfA and SSRS galaxy catalogs. We
show that if we apply the analysis in redshift space, both models reproduce
equally well the observed clustering of galaxies. Mass segregation is also
found in the models: more massive DHs are more clustered compared with less
massive ones. In redshift space, this mass segregation is reduced by a factor
2-3 due to the peculiar velocities. Observational catalogs give an indication
of luminosity and size segregation, which is consistent with the predictions of
the models. Because the mass segregation is smaller in redshift space, it is
suggestive that the real luminosity or size segregation of galaxies could be
significantly larger than what it is found in redshift catalogs.Comment: 13 pages including 9 figures (220 KB) in uuencoded compressed
Postscript format. To appear in The Astrophysical Journal, June 10. Latex
file and figures available at ftp://astrohp.ft.uam.es/pub/preprints/masse
Large Scale Morphological Segregation in Optically Selected Galaxy Redshift Catalogs
We present the results of an exhaustive analysis of the morphological
segregation of galaxies in the CfA and SSRS catalogs through the scaling
formalism. Morphological segregation between ellipticals and spirals has been
detected at scales up to 15-20 h Mpc in the CfA catalog, and up to 20-30
h Mpc in the SSRS catalog. Moreover, it is present not only in the
densest areas of the galaxy distribution, but also in zones of moderate
density.Comment: 9 pages, (1 figure included), uuencode compressed Postscript,
(accepted for publication in ApJ Letters), FTUAM-93-2
Analytic Solutions to Coherent Control of the Dirac Equation
A simple framework for Dirac spinors is developed that parametrizes
admissible quantum dynamics and also analytically constructs electromagnetic
fields, obeying Maxwell's equations, which yield a desired evolution. In
particular, we show how to achieve dispersionless rotation and translation of
wave packets. Additionally, this formalism can handle control interactions
beyond electromagnetic. This work reveals unexpected flexibility of the Dirac
equation for control applications, which may open new prospects for quantum
technologies
Dirac open quantum system dynamics: formulations and simulations
We present an open system interaction formalism for the Dirac equation.
Overcoming a complexity bottleneck of alternative formulations, our framework
enables efficient numerical simulations (utilizing a typical desktop) of
relativistic dynamics within the von Neumann density matrix and Wigner phase
space descriptions. Employing these instruments, we gain important insights
into the effect of quantum dephasing for relativistic systems in many branches
of physics. In particular, the conditions for robustness of Majorana spinors
against dephasing are established. Using the Klein paradox and tunneling as
examples, we show that quantum dephasing does not suppress negative energy
particle generation. Hence, the Klein dynamics is also robust to dephasing
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