For 10 points, name this constant of proportionality between the vacuum permittivity and the permittivity of its namesake kind of insulating material.
This quantity's value under the random phase approximation is given by the Lindhard function. Nitrided hafnium silicates belong to a class of materials named for having a high value for this quantity, which makes them useful in the fabrication of nanoscale MOSFET gates. This quantity is the dependent variable of the Kohlrausch-Williams-Watts and Havrilak-Negami relaxation models. This quantity alternates between high and low values in the layers of a (*) photonic crystal. This quantity minus one, divided by this quantity plus two, is proportional to molecular polarizability according to the Clausius-Mossotti relation. In non-magnetic materials, this quantity equals the square of the index of refraction. This dimensionless quantity equals one plus electric susceptibility and is denoted epsilon sub r. For 10 points, name this constant of proportionality between the vacuum permittivity and the permittivity of its namesake kind of insulating material.
This quantity's value under the random phase approximation is given by the Lindhard function.
dielectric constant [or  relative permittivity; accept absolute  permittivity before "minus one," but do not accept or prompt thereafter; prompt on "epsilon," "epsilon-sub-r," "kappa," or "k"]