4,725 research outputs found
Time-dependent Mechanics and Lagrangian submanifolds of Dirac manifolds
A description of time-dependent Mechanics in terms of Lagrangian submanifolds
of Dirac manifolds (in particular, presymplectic and Poisson manifolds) is
presented. Two new Tulczyjew triples are discussed. The first one is adapted to
the restricted Hamiltonian formalism and the second one is adapted to the
extended Hamiltonian formalism
Bianchi Cosmologies: New Variables and a Hidden Supersymmetry
We find a supersymmetrization of the Bianchi IX cosmology in terms of
Ashtekar's new variables. This provides a framework for connecting the recent
results of Graham and those of Ryan and Moncrief for quantum states of this
model. These states are also related with the states obtained particularizing
supergravity for a minisuperspace. Implications for the general theory are also
briefly discussed.Comment: 15 Pages, RevTex, NSF-ITP-93-9
The XMM spectral catalog of SDSS optically selected Seyfert 2 galaxies
We present an X-ray spectroscopic study of optically selected (SDSS) Seyfert
2 (Sy2) galaxies. The goal is to study the obscuration of Sy2 galaxies beyond
the local universe, using good quality X-ray spectra in combination with high
S/N optical spectra for their robust classification. We analyzed all available
XMM-Newton archival observations of narrow emission line galaxies that meet the
above criteria in the redshift range 0.05<z<0.35. We initially selected narrow
line AGN using the SDSS optical spectra and the BPT classification diagram. We
further modeled and removed the stellar continuum, and we analyzed the residual
emission line spectrum to exclude any possible intermediate-type Seyferts. Our
final catalog comprises 31 Sy2 galaxies with median redshift z~0.1. X-ray
spectroscopy is performed using the available X-ray spectra from the 3XMM and
the XMMFITCAT catalogs. Implementing various indicators of obscuration, we find
seven (~23%) Compton-thick AGN. The X-ray spectroscopic Compton-thick
classification agrees with other commonly used diagnostics, such as the X-ray
to mid-IR luminosity ratio and the X-ray to [OIII] luminosity ratio. Most
importantly, we find four (~13%) unobscured Sy2 galaxies, at odds with the
simplest unification model. Their accretion rates are significantly lower than
the rest of our Sy2 sample, in agreement with previous studies that predict the
absence of the broad line region below a certain Eddington ratio threshold.Comment: 12 pages, 6 figures, accepted for publication in A&
Contenido polínico de la familia Pinaceae en la atmósfera de Córdoba, España
XV lnternational A.P.L.E. Symposium of Palynolog
Dynamics of momentum entanglement in lowest-order QED
We study the dynamics of momentum entanglement generated in the lowest-order
QED interaction between two massive spin-1/2 charged particles, which grows in
time as the two fermions exchange virtual photons. We observe that the degree
of generated entanglement between interacting particles with initial
well-defined momentum can be infinite. We explain this divergence in the
context of entanglement theory for continuous variables, and show how to
circumvent this apparent paradox. Finally, we discuss two different
possibilities of transforming momentum into spin entanglement, through
dynamical operations or through Lorentz boosts.Comment: 10 pages and 7 figures. Accepted in PR
On the Hamilton-Jacobi Theory for Singular Lagrangian Systems
We develop a Hamilton-Jacobi theory for singular lagrangian systems using the
Gotay-Nester-Hinds constraint algorithm. The procedure works even if the system
has secondary constraints.Comment: 36 page
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