3,407,767 research outputs found
Comments on a Full Quantization of the Torus
Gotay showed that a representation of the whole Poisson algebra of the torus
given by geometric quantization is irreducible with respect to the most natural
overcomplete set of observables. We study this representation and argue that it
cannot be considered as physically acceptable. In particular, classically
bounded observables are quantized by operators with unbounded spectrum.
Effectively, the latter amounts to lifting the constraints that compactify both
directions in the torus.Comment: 10 pages. New "Discussion" section. References added. To appear in
IJMP
Non-circular features in Saturn's D ring: D68
D68 is a narrow ringlet located only 67,627 km (1.12 planetary radii) from
Saturn's spin axis. Images of this ringlet obtained by the Cassini spacecraft
reveal that this ringlet exhibits persistent longitudinal brightness variations
and a substantial eccentricity (ae=25+/-1 km). By comparing observations made
at different times, we confirm that the brightness variations revolve around
the planet at approximately the local orbital rate (1751.6 degrees/day), and
that the ringlet's pericenter precesses at 38.243+/-0.008 degrees/day,
consistent with the expected apsidal precession rate at this location due to
Saturn's higher-order gravitational harmonics. Surprisingly, we also find that
the ringlet's semi-major axis appears to be decreasing with time at a rate of
2.4+/-0.4 km/year between 2005 and 2013. A closer look at these measurements,
along with a consideration of earlier Voyager observations of this same
ringlet, suggests that the mean radius of D68 moves back and forth, perhaps
with a period of around 15 Earth years or about half a Saturn year. These
observations could place important constraints on both the ringlet's local
dynamical environment and the planet's gravitational field.Comment: 39 Pages, 11 Figures accepted for publication in Icarus Text slightly
modified to match corrections to proof
Legendre expansion of the neutrino-antineutrino annihilation kernel: Influence of high order terms
We calculate the Legendre expansion of the rate of the process up to 3rd order extending previous results
of other authors which only consider the 0th and 1st order terms. Using
different closure relations for the moment equations of the radiative transfer
equation we discuss the physical implications of taking into account quadratic
and cubic terms on the energy deposition outside the neutrinosphere in a
simplified model. The main conclusion is that 2nd order is necessary in the
semi-transparent region and gives good results if an appropriate closure
relation is used.Comment: 14 pages, 4 figures. To be published in A&A Supplement Serie
Submm-bright QSOs at z~2: signposts of co-evolution at high z
We have assembled a sample of 5 X-ray and submm-luminous z~2 QSOs which are
therefore both growing their central black holes through accretion and forming
stars copiously at a critical epoch. Hence, they are good laboratories to
investigate the co-evolution of star formation and AGN. We have performed a
preliminary analysis of the AGN and SF contributions to their UV-to-FIR SEDs,
fitting them with simple direct (disk), reprocessed (torus) and star formation
components. All three are required by the data and hence we confirm that these
objects are undergoing strong star formation in their host galaxies at rates
500-2000 Msun/y. Estimates of their covering factors are between about 30 and
90%. In the future, we will assess the dependence of these results on the
particular models used for the components and relate their observed properties
to the intrinsice of the central engine and the SF material, as well as their
relevance for AGN-galaxy coevolution.Comment: 6 pages, 2 figures, contributed talk to "Nuclei of Seyfert galaxies
and QSOs - Central engine & conditions of star formation" November 6-8, 2012.
MPIfR, Bonn, Germany. Po
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