A Dirac fermion can be analyzed as two Weyl fermions, with this quantity of the particle acting as a coupling constant between the chiralities. Unlike chirality, helicity is not Lorentz-invariant for particles with nonzero values of this quantity, as one (15[1])can boost to a frame going faster than the particle to reverse its (15[1])helicity. Mixing between flavor eigenstates and this quantity’s eigenstates causes (15[1])a process described by the PMNS (-5[1])matrix. The surface in k-space where the energy-momentum relation is satisfied is a (*) “shell” named after this (10[1])quantity. The oscillation (10[1])of neutrinos implies (10[1]-5[2])they do not have a (10[1])value of zero for this quantity, (10[2])as once thought. (10[1])A particle (10[1])is relativistic when its kinetic energy exceeds the energy due to this property of the particle. For 10 points, for a particle at rest, E equals what quantity times (10[1])c-squared? (10[1])■END■ (10[3])