4,113 research outputs found
VLBI observations of nearby radio loud Active Galactic Nuclei
We present an update of the parsec scale properties of the Bologna Complete
Sample consisting of 95 radio sources from the B2 Catalog of Radio Sources and
the Third Cambridge Revised Catalog (3CR), with z < 0.1. Thanks to recent new
data we have now parsec scale images for 76 sources of the sample. Most of them
show a one-sided jet structure but we find a higher fraction of two-sided
sources in comparison with previous flux-limited VLBI surveys. A few peculiar
sources are presented and discussed in more detail.Comment: 6 pages, 7 figures, Proceedings for "The Universe under the
Microscope" (AHAR 2008), April 2008, to be published in Journal of Physics:
Conference Series by Institute of Physics Publishing; R. Schoedel, A. Eckart,
S. Pfalzner, and E. Ros ed
Clan Properties in Parton Showers
By considering clans as genuine elementary subprocesses, i.e., intermediate
parton sources in the Simplified Parton Shower model, a generalized version of
this model is defined. It predicts analytically clan properties at parton level
in agreement with the general trends observed experimentally at hadronic level
and in Monte Carlo simulations both at partonic and hadronic level. In
particular the model shows a linear rising in rapidity of the average number of
clans at fixed energy of the initial parton and its subsequent bending for
rapidity intervals at the border of phase space, and approximate energy
independence of the average number of clans in fixed rapidity intervals. The
energy independence becomes stricter by properly normalizing the average number
of clans.Comment: (27 pages in Plain TeX plus 10 Postscript Figures, all compressed via
uufiles) DFTT 7/9
Maps of zeroes of the grand canonical partition function in a statistical model of high energy collisions
Theorems on zeroes of the truncated generating function in the complex plane
are reviewed. When examined in the framework of a statistical model of high
energy collisions based on the negative binomial (Pascal) multiplicity
distribution, these results lead to maps of zeroes of the grand canonical
partition function which allow to interpret in a novel way different classes of
events in pp collisions at LHC c.m. energies.Comment: 17 pages, figures (ps included); added references, some figures
enlarged. To appear in J. Phys.
Vector field localization and negative tension branes
It is shown that negative tension branes in higher dimensions may lead to an
effective lower dimensional theory where the gauge-invariant vector fields
associated with the fluctuations of the metric are always massless and
localized on the brane. Explicit five-dimensional examples of this phenomenon
are provided. Furthermore, it is shown that higher dimensional gauge fields can
also be localized on these configurations with the zero mode separated from the
massive tower by a gap.Comment: 16 pages, LaTeX style; to appear in Phys. Rev.
Non-topological gravitating defects in five-dimensional anti-de Sitter space
A class of five-dimensional warped solutions is presented. The geometry is
everywhere regular and tends to five-dimensional anti-de Sitter space for large
absolute values of the bulk coordinate. The physical features of the solutions
change depending on the value of an integer parameter. In particular, a set of
solutions describes generalized gravitating kinks where the scalar field
interpolates between two different minima of the potential. The other category
of solutions describes instead gravitating defects where the scalar profile is
always finite and reaches the same constant asymptote both for positive and
negative values of the bulk coordinate. In this sense the profiles are
non-topological. The physical features of the zero modes are discussed.Comment: 9 pages, 4 figure
Last scattering, relic gravitons and the circular polarization of the CMB
The tensor contribution to the -mode polarization induced by a magnetized
plasma at last scattering vanishes exactly. Conversely a polarized background
of relic gravitons cannot generate a -mode polarization. The reported
results suggest that, in the magnetized CDM paradigm, the dominant
source of circular dichroism stems from the large-scale fluctuations of the
spatial curvature.Comment: 8 pages, no figure
Plasma physics in clusters of galaxies
Clusters of galaxies are the largest self-gravitating structures in the
universe. Each cluster is filled with a large-scale plasma atmosphere, in which
primordial matter is mixed with matter that has been processed inside stars.
This is a wonderful plasma physics laboratory. Our diagnostics are the data we
obtain from X-ray and radio telescopes. The thermal plasma is a strong X-ray
source; from this we determine its density and temperature. Radio data reveal a
relativistic component in the plasma, and first measurements of the
intracluster magnetic field have now been made. Energization of the particles
and the field must be related to the cosmological evolution of the cluster. The
situation is made even richer by the few galaxies in each cluster which host
radio jets. In these galaxies, electrodynamics near a massive black hole in the
core of the galaxy lead to a collimated plasma beam which propagates from the
nucleus out to supergalactic scales. These jets interact with the cluster
plasma to form the structures known as radio galaxies. The interaction disturbs
and energizes the cluster plasma. This complicates the story but also helps us
understand both the radio jets and the cluster plasma.Comment: 12 pages, 6 figures, 3 in color. Invited review, to appear in Physics
of Plasmas, May 2003. After publication it can be found at
http://ojps.aip.org/po
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