Eli Waxman (Weizmann) gave a great lunch-time talk on the ultra-high energy neutrinos, the neutrino counterparts of ultra-high energy cosmic rays. He gave a nice argument that the CRs must come from incredibly luminous sources, based on their energies. My summary of this argument is that for any energy/charge, or potential, there is a corresponding power, or luminosity, V2/R. In CGS units, resistance has units of velocity, so the speed of light is a
fundamental resistance (ie, the impedance of free space). Of course, Waxman gives a physical explanation of this, not my mystical one, but the upshot is the same: Very high energy particles means very high potentials, and very high potentials mean very luminous sources or engines. Waxman, pretty convincingly, argues that the engines are probably gamma-ray bursts.
Waxman and the late John Bahcall (IAS) showed that this CR flux requires an ultra-high energy neutrino flux, and places a strong upper limit on the extragalactic neutrino flux over a wide range of energies. Interestingly, these ultra-high energy neutrinos will be detected by the next generation of detectors (Ice Cube and the like). If they come from GRBs, they will
point back to their sources and they will be prompt, ie, simultaneous with the photon burst (both niceties are true because neutrinos don't suffer magnetic deflections). Then Waxman will deserve a big prize.