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

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

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

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

Time-dependent gravitating solitons in five dimensional warped space-times

Time-dependent soliton solutions are explicitly derived in a five-dimensional theory endowed with one (warped) extra-dimension. Some of the obtained geometries, everywhere well defined and technically regular, smoothly interpolate between two five-dimensional anti-de Sitter space-times for fixed value of the conformal time coordinate. Time dependent solutions containing both topological and non-topological sectors are also obtained. Supplementary degrees of freedom can be also included and, in this case, the resulting multi-soliton solutions may describe time-dependent kink-antikink systems.Comment: 19 pages, 10 figure

Electric-magnetic duality and the conditions of inflationary magnetogenesis

The magnetogenesis scenarios triggered by the early variation of the gauge coupling are critically analyzed. In the absence of sources, it is shown that the electric and magnetic power spectra can be explicitly computed by means of electric-magnetic duality transformations. The remnants of a pre-inflationary expansion and the reheating process break explicitly electric-magnetic duality by inducing Ohmic currents. The generation of large-scale magnetic field and the physical distinction between electric and magnetic observables stems, in this class of models, from the final value reached by the conductivity of the plasma right after inflation. Specific numerical examples are given. The physical requirements of viable magnetogenesis scenarios are spelled out.Comment: 25 pages, 9 figure