That model yields a temperature-cubed dependence for heat capacity at low temperatures, and is named for Debye.
The anharmonicity of these particles is quantified by the Gruneisen parameter. Since these particles are always anharmonic in reality, they scatter off one another, with the scattering being elastic only at temperatures far below "theta-sub-D", where umklapp processes are frozen out. These particles have three independent polarizations, marking one difference in the analysis of a black-body-like model in which the namesake temperature "theta-sub-D" equals the ratio of Planck's constant to Boltzmann's constant, all times the maximum frequency of these collective excitations. That model yields a temperature-cubed dependence for heat capacity at low temperatures, and is named for Debye. For 10 points, name these quasiparticles that correspond to quantized vibrational modes of lattices.
The anharmonicity of these particles is quantified by the Gruneisen parameter.
phonons [prompt on "vibrations" or similar]