The conclusions of the Physics Working Group of the International Scoping Study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried out by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Super-beams, Laboratori Nazionali di Frascati, Rome, 21-26 June 2005) and NuFact06 (Ivine, CA, 24-30 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second-generation super-beam experiments, beta-beam facilities and the Neutrino Factory are evaluated and a quantitative comparison of the discovery potential of the three classes of facility is presented. High-precision studies of the properties of the muon are complementary to the study of neutrino oscillations. The Neutrino Factory has the potential to provide extremely intense muon beams and the physics potential of such beams is discussed in the final section of the report.

A possibility to measure sin 2 2θ 13 using reactor neutrinos is examined in detail. It is shown that the sensitivity sin 2 2θ 13 > 0.02 can be reached with 40 ton-year data by placing identical CHOOZlike detectors at near and far distances from a giant nuclear power plant whose total thermal energy is 24.3 GW th . It is emphasized that this measurement is free from the parameter degeneracies which occur in accelerator appearance experiments, and therefore the reactor measurement plays a role complementary to accelerator experiments. It is also shown that the reactor measurement may be able to resolve the degeneracy in θ 23 if sin 2 2θ 13 and cos 2 2θ 23 are relatively large.

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Doubly charged Higgs bosons (H ±± ) are a distinctive signature of the Higgs Triplet Model of neutrino mass generation. If H ±± is relatively light (m H ±± < 400 GeV) it will be produced copiously at the LHC, which could enable precise measurements of the branching ratios of the decay channels H ±± → l ± i l ± j . Such branching ratios are determined solely by the neutrino mass matrix which allows the model to be tested at the LHC. We quantify the dependence of the leptonic branching ratios on the absolute neutrino mass and Majorana phases, and present the permitted values for the channels e ± e ± , e ± µ ± and µ ± µ ± . It is shown that precise measurements of these three branching ratios are sufficient to extract information on the neutrino mass spectrum and probe the presence of CP violation from Majorana phases.