  This Letter of Intent (LoI) describes the outline and plan for the Neutrino
Telescope Array (NTA) project. High-energy neutrinos provide unique and
indisputable evidence for hadronic acceleration. Recently, IceCube has reported
astronomical neutrino candidates in excess of expectation from atmospheric
secondaries, but is limited by the water Cherenkov detection method. A next
generation high-energy neutrino telescope should be capable of establishing
indisputable evidence for cosmic high-energy neutrinos. It should not only have
orders-of-magnitude larger sensitivity, but also enough pointing accuracy to
probe known or unknown astronomical objects, without suffering from atmospheric
secondaries. The proposed installation is a large array of compound eye
stations of imaging atmospheric Cherenkov and fluorescence detectors, with wide
field of view and refined observational ability of air showers from cosmic tau
neutrinos in the PeV-EeV energy range. This advanced optical complex system is
based substantially on the development of All-sky Survey High Resolution
Air-shower detector (Ashra) and applies the tau shower Earth-skimming method to
survey PeV-EeV tau neutrinos. It allows wide (30 deg x 360 deg) and deep (~400
Mpc) survey observation for PeV-EeV tau neutrinos assuming the standard GRB
neutrino fluence.In addition, it enjoys the pointing accuracy of better than
0.2 deg in essentially background-free conditions. With the advanced imaging of
Earth-skimming tau showers in the wide field of view, we aim for clear
discovery and identification of astronomical tau neutrino sources, providing
inescapable evidence of the astrophysical hadronic model for acceleration
and/or propagation of extremely high energy protons in the precisely determined
direction.
