Letter of Intent: The Precision IceCube Next Generation Upgrade (PINGU)
  The Precision IceCube Next Generation Upgrade (PINGU) is a proposed low-energy in-fill array of the IceCube Neutrino Observatory. Leveraging technology proven with IceCube, PINGU will feature the world's largest effective volume for neutrinos at an energy threshold of a few GeV, improving the sensitivity to several aspects of neutrino oscillation physics at modest cost. With its unprecedented statistical sample of low-energy atmospheric neutrinos, PINGU will have highly competitive sensitivity to $\nu_{\mu}$ disappearance, the $\theta_{23}$ octant, and maximal mixing, will make the world's best $\nu_{\tau}$ appearance measurement, allowing a unique probe of the unitarity of the PMNS mixing matrix, and will be able to distinguish the neutrino mass ordering at $3\sigma$ significance with less than 4 years of data. PINGU can also extend the indirect search for solar WIMP dark matter complimentary to the on-going and planned direct dark matter experiments. At the lower end of the energy range, PINGU may use neutrino tomography to directly probe the composition of the Earth's core. With its increased module density, PINGU will improve IceCube's sensitivity to galactic supernova neutrino bursts and enable it to extract the neutrino energy spectral shape. 
The IceCube-PINGU Collaboration
physics.ins-det astro-ph.HE astro-ph.IM hep-ex