SCIENCE and MOTIVATION

There are a number of major issues which this workshop is aimed at:

• What is the origin of the ultra-high energy(PeV to ZeV) cosmic rays? Independently of whether there are super-GZK events or not, the CR flux levels near 1E20 eV from AGASA and HIRES are within 3 sigma of each other, and there is an intense debate about the possible astrophysical sources.
  What is the contribution to these from gamma-ray bursts, active galaxies, galactic core sources? Can we reconcile the AGASA and HIRES discrepancies? Can Fermi acceleration explain particles at the GZK limit, and can we test shock acceleration? How strong is the case for alternative astrophysical acceleration mechanisms? What are the implications of Auger\'s accumulating data, as the array progresses towards completion? What can be learned about intergalactic matter from cosmic ray propagation effects?
• What is the origin of GeV-TeV photons from AGN, GRB, SNRs? Are the jets in AGN and GRB hadronic or leptonic? What constraints can be imposed on these from TeV and correlated lower energy spectra and variability? What is the origin of the GeV-TeV emission from pulsars and possibly magnetars(polar cap or outer gap emittors?) Are there smoking gun signatures of Fermi(diffusive) or other, e.g. linear(wakefield, etc) acceleration of leptons? For scattering off magnetic turbulence, reconnection, etc? Is there strong evidence for proton acceleration and hadronic cascades? How realistic is it to detect gamma-ray signatures of the quantum-gravity energy scale, vacuum dispersion, etc., with GLAST, SWIFT, etc?
• What is the TeV to EeV neutrino emission of AGN, GRB, microquasars and other sources? How will it take for AMANDA to set limits on the diffuse neutrino flux from these? What can we learn about interactions at > TeV CM energies from atmospheric or point source neutrinos with Auger and ICECUBE? Can we detect UHE tau neutrinos, and what will we learn from them? How far can TeV-nu measurements constrain the neutrino masses, mixing angles, etc?

Of course, in a three week workshop not all of these topics can receive equal attention, and we intend to concentrate mainly on a few from each area, selected for maximum urgency as the workshop date approaches.

Incorporating UHE cosmic rays, neutrinos and gamma-rays under one umbrella makes for maximal science gains via cross-fertilization, since these three genres of cosmic signals are intimately linked from the fundamental physics point of view, while from the astrophysics side they facilitate the distinction of hadronic and electronic source signatures, as well as between source characteristics and propagation/intervening medium effects.

A workshop concentrating on the astrophysics of the sources and the physics of interactions in this ultra-high energy range is clearly topical from a theoretical perspective, as reflected in the prominence and abundance of papers from these fields in major astrophysics and physics journals, and the intensity of the associated science discussions in these communities.
It is also very timely from an experimental point of view because of the recent comissioning of, and data from, new experiments such as

• AUGER: Argentina/Chicago UHE CR array, already operating w. 400 tanks & 8 fluoresc. tel, taking data now; exp. 1600 tanks & 24 fluor.tel. by 05;
• HIRES: Fluorescence detector(Utah), on-line, stereo data expected, has several years of > GZK events AMANDA: UHE neutrino ice-Cherenkov detector, 0.05 km^3; already taking data and providing constraints on AGN, and soon GRB, models.
• MILAGRO: water Cherenkov, A=3,000 m^2, LANL, already taking data,