The flux suppression at the highest energies

Almost half a century ago, Greisen, Zatsepin and Kuz'min (GZK) predicted a "cosmologically meaningful termination" of the spectrum of cosmic rays at energies around $10^{20}$ eV due to their interaction with the cosmic microwave background, as they propagate from distant extragalactic sources. A suppression of the flux above $4\times 10^{19}$ eV is now confirmed. We argue that current data are insufficient to conclude whether the observed feature is due to energy loss during propagation, or else to the fact that the astrophysical accelerators reach their limit, or indeed to a combination of both source properties and propagation effects. We discuss the dependence of the spectral steepening upon the cosmic-ray composition, source properties, and intervening magnetic fields, and speculate on the additional information that may be necessary to reach unambiguous conclusions about the origin of the flux suppression and of the mechanisms behind the acceleration of cosmic rays up to the highest observed energies.Comment: Invited review prepared for Comptes Rendus Physique (2014), in pres

Charmless B Decays at CDF

he CDF experiment at the Fermilab Tevatron p-pbar collider pioneered the exploration of charmless b-hadron decays in hadron collisions. This provided a unique, rich and highly successful program of measurements that is currently reaching its full maturity. I report here results on two-body decays and the new analysis of B0s-->phiphi decays in a event sample corresponding to 2.9 fb-1.Comment: 7 pages, 4 figures, part of the proceedings of the BEAUTY2009 conference. Introduction slightly changed. Minor corrections in other text. References adde

Strategy-proof allocation mechanisms for economies with public goods

This paper provides a characterization of the class of incentive compatible (i.e., strategy-proof) allocation mechanisms for decision problems associated with classical economic environments. It is shown that when at least one public good is provided, then only dictatorial allocation mechanisms are incentive compatible. Dictatorial mechanisms are very unsatisfactory, as any conflict of interest is always resolved in favor of a single individual (the dictator). This result reveals a basic incompatibility between incentive compatibility and any other desirable property (e.g., any kind of efficiency, fairness, etc.) of an allocation mechanism. In particular, incentive compatible allocation mechanisms typically produce inefficient outcomes

Strategy-proof allocation mechanisms for pure public goods economies when preferences are monotonic

A fundamental problem in public finance is that of allocating a␣given budget to financing the provision of public goods (education, transportation, police, etc.). In this paper it is established that when␣admissible preferences are those representable by continuous and increasing utility functions, then strategy-proof allocation mechanisms whose (undominated) range contains three or more outcomes are dictatorial on the set of profiles of strictly increasing utility functions, a dense subset of the domain in the topologies commonly used in this context. If admissible utility functions are further restricted to be strictly increasing, or if mechanisms are required to be non-wasteful, then strategy-profness leads to (full) dictatorship.Publicad

Multiwavelength Gamma-Ray Bursts Observations with ECLAIRs

ECLAIRs is the next space borne instrument that will be fully dedicated to multi-wavelength studies of Gamma-Ray Bursts (GRBs). It consists of a coded mask telescope with a wide (~2 sr) field of view, made of 6400 CdTe pixels (~1000 cm^2), which will work in the 4-300 keV energy band. It is expected to localise ~80 GRBs/yr, thanks to the on-board real time event processing. The GRBs (and other transients) coordinates will be distributed within a few seconds from the onset of the burst with a typical uncertainty of ~5-10 arcmin. The detection system will also include a soft X-ray camera (1-10 keV) allowing to study in detail the prompt soft X-ray emission and to reduce the error box for about half of the GRBs seen by ECLAIRs to ~30 arcsec. ECLAIRs is expected to be flown in late 2011 and to be the only instrument capable of providing GRB triggers with sufficient localisation accuracy for GRB follow-up observations with the powerful ground based spectroscopic telescopes available by then. We will present the current status of the ECLAIRs project and its possible developments.Comment: 6 pages, 1 figure, proceedings of the Cefalu Astrophysical Conference, 11-24 June 200