Development of telescopes for extremely energetic neutrinos: AMANDA, ANITA, and ARIANNA

Dedicated high-energy neutrino telescopes based on optical Cherenkov techniques have been scanning the cosmos for about a decade. At TeV scales, limits on the diffuse flux have improved by several orders of magnitude, eliminating the most optimistic models that tend to be normalized to the extragalactic X-ray or gamma-ray luminosity. At higher energies, neutrino telescopes have provided the first flux limits from point sources and diffusely distributed sources such as cosmogenic neutrinos generated by the GZK process, whose existence is relatively secure but whose predicted flux is frustratingly small. To substantially improve the experimental capabilities at the very highest energies, new techniques are required. I will briefly discuss preliminary results from the radio-based Cherenkov detector ANITA, and describe a new concept called ARIANNA that promises to increase the sensitivity to neutrinos with energies in excess of 1017 eV. Radio Cherenkov telescopes have already ruled out some of the more exotic predictions for neutrino intensity and may soon test more conventional GZK models. In addition to flux measurements, these devices can probe for non-standard particle physics by investigating the neutrino cross-section.