21,073 research outputs found
Local continuity laws on the phase space of Einstein equations with sources
Local continuity equations involving background fields and variantions of the
fields, are obtained for a restricted class of solutions of the
Einstein-Maxwell and Einstein-Weyl theories using a new approach based on the
concept of the adjoint of a differential operator. Such covariant conservation
laws are generated by means of decoupled equations and their adjoints in such a
way that the corresponding covariantly conserved currents possess some
gauge-invariant properties and are expressed in terms of Debye potentials.
These continuity laws lead to both a covariant description of bilinear forms on
the phase space and the existence of conserved quantities. Differences and
similarities with other approaches and extensions of our results are discussed.Comment: LaTeX, 13 page
A Hamiltonian functional for the linearized Einstein vacuum field equations
By considering the Einstein vacuum field equations linearized about the
Minkowski metric, the evolution equations for the gauge-invariant quantities
characterizing the gravitational field are written in a Hamiltonian form by
using a conserved functional as Hamiltonian; this Hamiltonian is not the analog
of the energy of the field. A Poisson bracket between functionals of the field,
compatible with the constraints satisfied by the field variables, is obtained.
The generator of spatial translations associated with such bracket is also
obtained.Comment: 5 pages, accepted in J. Phys.: Conf. Serie
High-dimensional neutrino masses
For Majorana neutrino masses the lowest dimensional operator possible is the
Weinberg operator at . Here we discuss the possibility that neutrino
masses originate from higher dimensional operators. Specifically, we consider
all tree-level decompositions of the , and neutrino mass
operators. With renormalizable interactions only, we find 18 topologies and 66
diagrams for , and 92 topologies plus 504 diagrams at the level. At
there are already 576 topologies and 4199 diagrams. However, among all
these there are only very few genuine neutrino mass models: At we
find only (2,2,2) genuine diagrams and a total of (2,2,6) models. Here, a model
is considered genuine at level if it automatically forbids lower order
neutrino masses {\em without} the use of additional symmetries. We also briefly
discuss how neutrino masses and angles can be easily fitted in these
high-dimensional models.Comment: Coincides with published version in JHE
Dissecting the Power Sources of Low-Luminosity Emission-Line Galaxy Nuclei via Comparison of HST-STIS and Ground-Based Spectra
Using a sample of ~100 nearby line-emitting galaxy nuclei, we have built the
currently definitive atlas of spectroscopic measurements of H_alpha and
neighboring emission lines at subarcsecond scales. We employ these data in a
quantitative comparison of the nebular emission in Hubble Space Telescope (HST)
and ground-based apertures, which offer an order-of-magnitude difference in
contrast, and provide new statistical constraints on the degree to which
Transition Objects and low-ionization nuclear emission-line regions (LINERs)
are powered by an accreting black hole at <10 pc. We show that while the
small-aperture observations clearly resolve the nebular emission, the aperture
dependence in the line ratios is generally weak, and this can be explained by
gradients in the density of the line-emitting gas: the higher densities in the
more nuclear regions potentially flatten the excitation gradients, suppressing
the forbidden emission. The Transition Objects show a threefold increase in the
incidence of broad H_alpha emission in the high-resolution data, as well as the
strongest density gradients, supporting the composite model for these systems
as accreting sources surrounded by star-forming activity. The narrow-line
LINERs appear to be the weaker counterparts of the Type 1 LINERs, where the low
accretion rates cause the disappearance of the broad-line component. The
enhanced sensitivity of the HST observations reveals a 30% increase in the
incidence of accretion-powered systems at z~0. A comparison of the strength of
the broad-line emission detected at different epochs implies potential
broad-line variability on a decade-long timescale, with at least a factor of
three in amplitude.Comment: 27 pages, 13 figures, 4 tables, accepted for publication in Ap
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