Clan structure analysis and new physics signals in pp collisions at LHC

The study of possible new physics signals in global event properties in pp collisions in full phase space and in rapidity intervals accessible at LHC is presented. The main characteristic is the presence of an elbow structure in final charged particle MD's in addition to the shoulder observed at lower c.m. energies.Comment: 9 pages, talk given at Focus on Multiplicity (Bari, Italy, June 2004

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

Scenarios for multiplicity distributions in pp collisions in the TeV energy region

Possible scenarios based on available experimental data and phenomenological knowledge of the GeV energy region are extended to the TeV energy region in the framework of the weighted superposition mechanism of soft and semi-hard events. KNO scaling violations, forward-backward multiplicity correlations, Hq vs. q oscillations and shoulder structures are discussed.Comment: 10 pages, 10 figures, talk given at "Focus on Multiplicity" (Bari, Italy, June 2004

A double radio halo in the close pair of galaxy clusters Abell 399 and Abell 401

Radio halos are faint radio sources usually located at the center of merging clusters of galaxies. These diffuse radio sources are rare, having so far been found only in about 30 clusters of galaxies, suggesting that particular conditions are needed to form and maintain them. It is interesting to investigate the presence of radio halos in close pairs of interacting clusters in order to possibly clarify their origin in relation to the evolutionary state of the merger. In this work, we study the case of the close pair of galaxy clusters A399 and A401. A401 is already known to contain a faint radio halo, while a hint of diffuse emission in A399 has been suggested based on the NVSS. To confirm this possibility, we analyzed deeper Very Large Array observations at 1.4 GHz of this cluster. We find that the central region of A399 is permeated by a diffuse low-surface brightness radio emission that we classify as a radio halo with a linear size of about 570 kpc and a central brightness of 0.3 micro-Jy/arcsec^2. Indeed, given their comparatively small projected distance of about 3 Mpc, the pair of galaxy clusters A401 and A399 can be considered as the first example of double radio halo system. The discovery of this double halo is extraordinary given the rarity of these radio sources in general and given that current X-ray data seem to suggest that the two clusters are still in a pre-merger state. Therefore, the origin of the double radio halo is likely to be attributed to the individual merging histories of each cluster separately, rather than to the result of a close encounter between the two systems.Comment: 6 pages, 4 figures, accepted for publication in A&

Halo and Relic Sources in Clusters of Galaxies

New images of 7 radio halos and relics, obtained with the Very Large Array at 20 or 90 cm, are presented here. The existence of a cluster-wide radio halo in the clusters A 665 and CL 0016+16 is confirmed. Both these clusters share the properties of the other clusters with radio halos, i.e. are luminous in X-rays, have high temperature, and show recent merger processes. No diffuse sources are detected in a sample of clusters showing at least a tailed radio galaxy within 300 kpc from the cluster center, indicating that the connection between tailed radio galaxies and halos is not relevant. For these clusters we give limits to the surface brightness and to the angular size of possible undetected diffuse sources.Comment: 16 Figures in separated files. A large ps file with figures (gg-aug00.ps.gz) in the text is avaialble at ftp://terra.bo.cnr.it/papers/journals New Astronomy Vol. 5, p.335, in pres

Particle reacceleration in Coma cluster: radio properties and hard X-ray emission

The radio spectral index map of the Coma halo shows a progressive steepening of the spectral index with increasing radius. Such a steepening cannot be simply justified by models involving continuous injection of fresh particles in the Coma halo or by models involving diffusion of fresh electrons from the central regions. We propose a {\it two phase} model in which the relativistic electrons injected in the Coma cluster by some processes (starbursts, AGNs, shocks, turbulence) during a {\it first phase} in the past are systematically reaccelerated during a {\it second phase} for a relatively long time ($\sim$ 1 Gyr) up to the present time. We show that for reacceleration time scales of $\sim 0.1$ Gyr this hypothesis can well account for the radio properties of Coma C. For the same range of parameters which explain Coma C we have calculated the expected fluxes from the inverse Compton scattering of the CMB photons finding that the hard X-ray tail discovered by BeppoSAX may be accounted for by the stronger reacceleration allowed by the model. The possibility of extending the main model assumptions and findings to the case of the other radio haloes is also discussed, the basic predictions being consistent with the observations.Comment: 15 pages, 13 figures, accepted for publication in MNRA

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.