Ultra High Energy Cosmic Rays from charged black holes. A new theoretical possibility?

In General Relativity, there is a new field of activity concerning the study of charged stars. In a recent paper, Ray et al. have shown the possibility that the collapse of a charged star could form a charged black hole before all the charge leaves the system. In this field of view we propose a new model for UHECR and we will show that it is possible to accelerate cosmic rays up to EeV. In this talk we will compute the UHECR flux, the charged black hole density and the energy spectrum associated with them in order to reproduce experimental data. We will see that we need only a small number of these hidden sources in order to account for observed UHECR properties and we will study the limits on charge and mass of black holes.Comment: 4 pages, 2 figure

On the role of galactic magnetic halo in the ultra high energy cosmic rays propagation

The study of propagation of Ultra High Energy Cosmic Rays (UHECR) is a key step in order to unveil the secret of their origin. Up to now it was considered only the influence of the galactic and the extragalactic magnetic fields. In this article we focus our analysis on the influence of the magnetic field of the galaxies standing between possible UHECR sources and us. Our main approach is to start from the well known galaxy distribution up to 120 Mpc. We use the most complete galaxy catalog: the LEDA catalog. Inside a sphere of 120 Mpc around us, we extract 60130 galaxies with known position. In our simulations we assign a Halo Dipole magnetic Field (HDF) to each galaxy. The code developed is able to retro-propagate a charged particle from the arrival points of UHECR data across our galaxies sample. We present simulations in case of Virgo cluster and show that there is a non negligible deviation in the case of protons of $7 \times 10^{19}$ eV, even if the $B$ value is conservative. Then special attention is devoted to the AGASA triplet where we find that NGC3998 and NGC3992 could be possible candidates as sources.Comment: Version accepted from ApJ, 5 figure

Rayons cosmiques de très haute énergie ( vers une nouvelle astronomie)

Les rayons cosmiques ont joué un rôle important dans l histoire de la Physlque depuis plus d'un siècle. Leur spectre s'étend pour plus de 10 ordres de grandeur. La présence du rayonnement de fond diffus cosmologique limite la distance de propagation et définit la classe des rayons cosmiques d'énergie ultra-haute (appelés UHECR) qui ont une énergie au-delà du seuil de production de pions, encore appelée coupure GZK. Les aspects généraux du problème sont analysés de façon critique. Je décris donc une méthode de reconstruction des trajectoires des UHECR dans I'univers proche, en partant du champ magnétique Galactique. Le code développé est capable de rétro-propager des particules chargées dans un champ magnétique quelconque. Le champ magnétique Galactique est reconstruit à travers les modèles actuels. Pour déterminer Ie champ magnétique extragalactique, j'ai utilisé une carte de I'univers local, extraite du catalogue HyperLEDA. Pour vérifier les effets de ces champs, j'ai rétro-propagé un faisceau de 40000 protons, d'un degré de rayon, dans la direction de I'amas de la Vierge. La déviation moyenne n'est pas négligeable. J'ai appliqué la même méthode à I'évènement triple de I'expérience AGASA auquel j'ai ajouté un quatrième évènement de HiRes. Parmi les sources possibles, j'ai identifié NGC3998, un noyau actif de galaxies, de la catégorie LINER, bon candidat pour I'accélération. Enfin, j'ai travaillé aussi sur un nouveau type de source: les trous noirs chargés, qui pourraient être a I'origine d'une émission de particules de très haute énergie. J'en décris Ie mécanisme d'accélération et Ie flux attendu, en suggérant une corrélation avec les sursauts gamma. Je propose donc une stratégie de reconstruction de trajectoires qui pourra être améliorée avec les prochaines expériences (AUGER, SKA, LOFAR) ainsi qu'une nouvelle source à rechercher a travers ce nouveau type d'astronomieCosmic rays play an important role in the history of Physics, since more tan a century. Their spectrum extends by more than 10 orders of magnitude. The cosmic background radiation constrains the propagation distance and defines the class of Ultra High Energy Cosmic Rays (UHECR) which carry energy well beyond the pion production threshold, called cutoff GZK. Several experiments studied the UHECR to understand their nature and origin. The general aspects of this problems are analyzed in a critical flavor. I describe a method for the reconstruction of UHECR trajectories within the local universe, starting from the Galactic Magnetic Field (GMF). My code is able to back-propagate charged particles in a magnetic field. To determine the extragalactic magnetic field, I used a local universe map, taken from the catalog HyperLEDA. To verify the effects of these fields on UHECR trajectories, I back-propagate a beam of 40000 protons, 1 degree wide, towards the direction of Virgo cluster. The mean deviation is 0.780 . and grows up to 1.30 for a frozen field model. These values are not negligible. I applied the same method to the triple event of AGASA experiment, added of a fourth event from HiRes. Through the plausible sources, I identified NGC3998, an Active Galactic Nucleus, of LINER type, a good candidate for acceleration. Finally, I worked also on a new kind of source: the charged black holes, which can be at the origin of UHECR emission. I sketch the acceleration mechanism and the expected flux, suggesting a correlation with gamma-ray bursts. So I propose a strategy of trajectory reconstruction, which can be improved with the next generation experiments (AUGER, SKA, LOFAR), as well as a new source to be searches through this new kind of astronomyCHAMBERY -BU Bourget (730512101) / SudocSudocFranceF

Ricerca sociale ed emancipazione. Campi, posizionamenti e pratiche

Negli Stati Uniti E.O. Wright ha proposto una scienza sociale ‘emancipativa’ espressamente rivolta a legittimare forme di critica al tardocapitalismo contemporaneo, per comprendere e dare visibilità a forme possibili di contro-organizzazione sociale, e generare così una conoscenza scientifica in grado di sfidare forme emergenti di sfruttamento. In America Latina si moltiplicano nelle università nuove ‘ecologie’ di saperi, cioè percorsi didattici e di ricerca in chiave radicalmente pluridisciplinare legati a istanze poste dai cittadini, secondo pratiche di interazione non dissimili dall’idea di ‘ricerca sociale democratica’ portata avanti a Mumbai da A. Appadurai. Ma anche in Europa, B. de Sousa Santos, L. Boltanski e molti altri provano a tradurre in futuro gli approcci della sociologia critica che caratterizzarono i decenni centrali del ’900 e che già indicavano nei pubblici plurali di cui si compone la società – più che nei circuiti ristretti dei colleghi – gli interlocutori privilegiati per la costruzione del disegno di ricerca e la gestione della vita sociale dei dati prodotti. Oggi tutto ciò avviene, però, con la marcata consapevolezza che occorra promuovere una nuova stagione di ‘risoggettivazione reciproca’ tra ricercatori e attori sociali che passi anche attraverso la capacità immergersi e lasciarsi interpellare dalla dimensione narrativa, esperienziale, esistenziale di processi sociali invisibili, turbolenti, scomodi, difficilmente accessibili, ma in qualche modo emblema profondo dell’attuale complessità