Effect of fluctuating inertial forces on the critical dynamics of a pure fluid

A calculation is carried out of the effect of imposed inertial forces on the critical dynamics of a pure fluid near the liquid-vapor critical point. The mechanism for the relaxation of the critical fluctuations of the order parameter is the Brownian motion in the long wavelength hydrodynamic shear modes. The additional fluctuating inertial forces add noise to these modes, leading to an increase inγ_q, the order parameter relaxation rate for a fluctuation of wave number q. A general formula is derived for Δ γ_q/γ_q, the fractional increase in relaxation rate, in terms of the acceleration power spectral density. The predicted strong dependences on temperature, angle, and q provide crucial tests for the theory.