Fluctuating hydrodynamics of smectic-Aliquid crystals

In addition to bulk viscosities that diverge as 1/ω, Mazenko, Ramaswamy, and Toner have predicted that smectic-A liquid crystals will have shear viscosities with (1) divergent real parts—implying no flow below a minimum yield stress—and (2) divergent imaginary parts—implying glassy behavior. In this Letter it is shown that smectic-A liquid crystals are neither ‘‘Bingham plastics’’ nor ‘‘glasses.’’ The finiteness of ${\mathrm{\eta }}_2$ to all orders of perturbation theory is proven, and the relevant cancellations to one-loop order are displayed.