Possible solutions to a problem regarding these particles are given in the “Normal” and “Inverted” Hierarchies. Two W-minus bosons exchange one of these particles in a proposed mechanism sought after by the EXO-200 experiment. In a parametrization of these particles, a free quantity characterizing CP-violation is represented by the phase factor “delta,” which appears along with three angles in the PMNS matrix. Two down quarks are converted into up quarks (15[1])with the release of electrons in a hypothetical form of (*) double beta decay that does not produce these particles in which they are required to be their own antiparticle. Because they don’t interact with any force except (10[1])gravity, right-handed versions of these particles are called “sterile.” (10[1])For 10 points, identify these leptons whose name comes from a combination of their low mass and zero charge. (10[1])■END■