We assume there to be precisely three left-handed neutrino states whose Majorana masses are generated by an unspecified mechanism. Were CP conserved, the symmetric neutrino mass matrix M would be real and all six of its distinct entries could be experimentally determined. But CP is not conserved so that M is likely to be complex. As a result, not all nine of its convention-independent real parameters can be determined without an appeal to theory. Thus we examine the possibility that a restricted class of neutrino mass matrices may suffice to describe current data, namely those complex symmetric matrices several of whose entries vanish. We find that there are seven acceptable textures with two independent zeroes, and we explore their contrasting phenomenological implications.Textures with more than two independent zeroes appear to be excluded by experiment. 01/02

We identify three independent two-fold parameter degeneracies (δ , θ 13 ), sgn(δm 2 31 ) and (θ 23 , π/2 − θ 23 ) inherent in the usual three-neutrino analysis of long-baseline neutrino experiments, which can lead to as much as an eight-fold degeneracy in the determination of the oscillation parameters. We discuss the implications these degeneracies have for detecting CP violation and present criteria for breaking them. A superbeam facility with a baseline at least as long as the distance between Fermilab and Homestake (1290 km) and a narrow band beam with energy tuned so that the measurements are performed at the first oscillation peak can resolve all the ambiguities other than the (θ 23 , π/2 − θ 23 ) ambiguity (which can be resolved at a neutrino factory) and a residual (δ , π − δ) ambiguity. However, whether or not CP violation occurs in the neutrino sector can be ascertained independently of the latter two ambiguities. The (δ , π − δ) ambiguity can be eliminated by performing a second measurement to which only the cos δ terms contribute. The hierarchy of mass eigenstates can be determined at other oscillation peaks only in the most optimistic conditions, making it necessary to use the first oscillation maximum. We show that the degeneracies may severely compromise the ability of the proposed SuperJHF-HyperKamiokande experiment to establish CP violation. In our calculations we use approximate analytic expressions for oscillation probabilitites that agree with numerical solutions with a realistic Earth density profile. * The misconception that the cos δ term dominates at large L and E ν comes from extending the large E ν approximation beyond its range of validity, as discussed in Ref. [18].

Searches for dark matter scattering off nuclei are typically compared assuming that the dark matter's spin-independent couplings are identical for protons and neutrons. This assumption is neither innocuous nor well motivated. We consider isospin-violating dark matter (IVDM) with one extra parameter, the ratio of neutron to proton couplings, and include the isotope distribution for each detector. For a single choice of the coupling ratio, the DAMA and CoGeNT signals are consistent with each other and with current XENON constraints, and they unambiguously predict near future signals at XENON and CRESST. We provide a quark-level realization of IVDM as WIMPless dark matter that is consistent with all collider and low-energy bounds. PACS numbers: 95.35.+d, 12.60.Jv Introduction.Dark matter makes up five-sixths of the matter in the Universe, but all current evidence for dark matter is through its gravitational effects. The detection of dark matter scattering through non-gravitational interactions would be a large step toward identifying dark matter, and there are many experiments searching for such events. The excitement around this approach has been heightened recently by data from the DAMA [1] and CoGeNT [2] experiments, which are consistent with scattering by a dark matter particle with mass m X ∼ 10 GeV and spin-independent (SI) X-nucleon scattering cross sections σ N ∼ 2×10 −4 pb and 5 × 10 −5 pb, respectively. This excitement is, however, tempered by null results from XENON [3,4] and CDMS [5,6], leaving a confusing picture that has motivated much theoretical and experimental work.

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