In the context of three-neutrino oscillations, we study the possibility of using antineutrinos from nuclear reactors to explore the 10 −4 eV 2 < ∆m 2 ⊙ ∼ < 8 × 10 −4 eV 2 region of the LMA MSW solution of the solar neutrino problem and measure ∆m 2 ⊙ with high precision. The KamLAND experiment is not expected to determine ∆m 2 ⊙ if the latter happens to lie in the indicated region. By analysing both the total event rate suppression and the energy spectrum distortion caused byν e oscillations in vacuum, we show that the optimal baseline of such an experiment is L ∼ (20 − 25) km. Furthermore, for 10 −4 eV 2 < ∆m 2 ⊙ ∼ < 5 × 10 −4 eV 2 , the same experiment might be used to try to distinguish between the two possible types of neutrino mass spectrum -with normal or with inverted hierarchy, by exploring the effect of interference between the atmospheric-and solar-∆m 2 driven oscillations; for larger values of ∆m 2 ⊙ not exceeding 8.0 × 10 −4 eV 2 , a shorter baseline, L ∼ = 10 km, would be needed for the purpose. The indicated interference effect modifies in a characteristic way the energy spectrum of detected events. Distinguishing between the two types of neutrino mass spectrum requires, however, a high precision determination of the atmospheric ∆m 2 , a sufficiently large sin 2 θ and a nonmaximal sin 2 2θ ⊙ , where θ and θ ⊙ are the mixing angles respectively limited by the CHOOZ and Palo Verde data and characterizing the solar neutrino oscillations. It also requires a relatively high precision measurement of the positron spectrum in the reactionν e + p → e + + n.

We study fermion masses and mixing angles, including the generation of a seesaw mechanism for the neutrinos, in extended technicolor (ETC) theories. We formulate an approach to these problems that relies on assigning righthanded Q = −1/3 quarks and charged leptons to ETC representations that are conjugates of those of the corresponding left-handed fermions. This leads to a natural suppression of these masses relative to the Q = 2/3 quarks, as well as the generation of quark mixing angles, both long-standing challenges for ETC theories. Standard-model-singlet neutrinos are assigned to ETC representations that provide a similar suppression of neutrino Dirac masses, as well as the possibility of a realistic seesaw mechanism with no mass scale above the highest ETC scale of roughly 10 3 TeV. A simple model based on the ETC group SU(5) is constructed and analyzed. This model leads to non-trivial, but not realistic mixing angles in the quark and lepton sectors. It can also produce sufficiently light neutrinos, although not simultaneously with a realistic quark spectrum. We discuss several aspects of the phenomenology of this class of models.14.60. PQ, 12.60.Nz, 14.60.St *

The Sp(4) gauge theory with two Dirac fundamental flavours provides a candidate for the microscopic origin of composite-Higgs models based on the SU (4)/Sp(4) coset. We employ a combination of two different, complementary strategies for the numerical lattice calculations, based on the Hybrid Monte Carlo and on the Heat Bath algorithms. We perform pure Yang-Mills, quenched computations and exploratory studies with dynamical Wilson fermions.We present the first results in the literature for the spectrum of glueballs of the pure Sp(4) Yang-Mills theory, an EFT framework for the interpretation of the masses and decay constants of the lightest pion, vector and axial-vector mesons, and a preliminary calculation of the latter in the quenched approximation. We show the first numerical evidence of a bulk phase transition in the lattice theory with dynamical Wilson fermions, and perform the technical steps necessary to set up future investigations of the mesonic spectrum of the full theory.

We perform lattice studies of meson mass spectra and decay constants of the Sp(4) gauge theory in the quenched approximation. We consider two species of (Dirac) fermions as matter field content, transforming in the 2-index antisymmetric and the fundamental representation of the gauge group, respectively. All matter fields are formulated as Wilson fermions. We extrapolate to the continuum and massless limits, and compare to each other the results obtained for the two species of mesons. In the case of two fundamental and three antisymmetric fermions, the long-distance dynamics is relevant for composite Higgs models. This is the first lattice study of this class of theories. The global SU (4) × SU (6) symmetry is broken to the Sp(4) × SO(6) subgroup, and the condensates align with the explicit mass terms present in the lattice formulation of the theory.The main results of our quenched calculations are that, with fermions in the 2-index antisymmetric representation of the group, the masses squared and decay constant squared of all the mesons we considered are larger than the corresponding quantities for the fundamental representation, by factors that vary between ∼ 1.2 and ∼ 2.7. We also present technical results that will be useful for future lattice investigations of dynamical simulations, of composite chimera baryons, and of the approach to large-N in the Sp(2N ) theories considered. We briefly discuss their high-temperature behaviour, where symmetry restoration and enhancement are expected. We acknowledge useful discussions withWe summarise in this Appendix our conventions in the treatment of spinors, which are useful, for example, in switching between the 2-component and the 4-component notation (see also Ref. [50]). The former is best suited to highlight the symmetries of the system, while the latter is the formalism adopted as a starting point for the lattice numerical