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Neutrino-nucleus elastic scattering (νAel) provides a unique laboratory to study the quantum-mechanical (QM) coherency effects in electroweak interactions. The deviations of the cross sections from those of completely coherent systems can be quantitatively characterized through a coherency parameter α(q²). The relations between α and the underlying nuclear physics in terms of nuclear form factors are derived. The dependence of cross section on α(q²) for the various neutrino sources is presented. The α(q²) values are evaluated from the measured data of the COHERENT CsI and Ar experiments. Complete coherency and decoherency conditions are excluded by the CsI data with p=0.004 at q²=3.1×10³ MeV² and p=0.016 at q²=2.3×10³ MeV², respectively, verifying that both QM superpositions and nuclear many-body effects contribute to νAel interactions. [ABSTRACT FROM AUTHOR]

Relativistic millicharged particles (χq) have been proposed in various extensions to the standard model of particle physics. We consider the scenarios where they are produced at nuclear reactor core and via interactions of cosmic rays with the Earth's atmosphere. Millicharged particles could also be candidates for dark matter and become relativistic through acceleration by supernova explosion shock waves. The atomic ionization cross section of χq with matter are derived with the equivalent photon approximation. Smoking-gun signatures with significant enhancement in the differential cross section are identified. New limits on the mass and charge of χq are derived, using data taken with a point-contact germanium detector with 500 g mass functioning at an energy threshold of 300 eV at the Kuo-Sheng Reactor Neutrino Laboratory. [ABSTRACT FROM AUTHOR]

Constraints on couplings of several beyond-Standard-Model-physics scenarios, mediated by massive intermediate particles including (1) an extra Z-prime, (2) a new light spin-1 boson, and (3) a charged Higgs boson, are placed via the neutrino-electron scattering channel to test the Standard Model at a low energy-momentum transfer regime. Data on νe-e and νe-e scattering from the TEXONO and LSND, respectively, are used. Upper bounds to coupling constants of the flavor-conserving and flavor-violating new light spin-1 boson and the charged Higgs boson with respect to different mediator masses are determined. The relevant parameter spaces are extended by allowing light mediators. New lower mass limits for extra Z-prime gauge boson models are also placed. [ABSTRACT FROM AUTHOR]