Neutrino opacities for high (left panel) and moderate (right panel) mass density. In each panel, for neutrinos (solid lines) and antineutrinos (dashed lines), we plot, vs. neutrino energy ε, the absorption opacity (χ and ﹩\bar{\chi };﹩ red lines), the elastic (isoenergetic) scattering opacity (σ_IS and ﹩{\bar{\sigma }}_{{\rm\small{IS}}};﹩ blue lines), the NES opacity (χ_SC and ﹩{\bar{\chi }}_{{\rm{S}}{\rm\small{C}}};﹩ green lines), and the opacity due to pair creation and annihilation (χ_TP and ﹩{\bar{\chi }}_{{\rm{T}}{\rm\small{P}}};﹩ black lines). The NES and pair creation and annihilation opacities were computed with the neutrino and antineutrino number densities set to zero; see Equations (17) and (19).