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The renormalization-group equations for critical behavior in 4a dimensions are generalized to the discussion of dynamic exponents at T = T, and then applied to a situation recently considered by Hohenberg, Halperin, and Ma (HHM); namely, one in which an n-component primary field Q is coupled to a secondary field q via a Q(QQ)cp coupling. In this work their analysis of relaxational fields is explicitly considered at order &'. For n (4, we find the dynamic exponents differ in one case at 0(&') from that given by HHM. In contrast to HHM, the dynamic scaling postulate is also preserved by the second-order fixed points in all instances and detailed analysis is given. The fixed-point values of R, a dimensionless ratio of relaxation rates for the q and Q fields, in certain cases, is found to go as R» -1/a, which is a new result. This large value where it occurs is found essential to understanding dynamic scaling. Analysis of the case of a propagating conserved q field also is given. It is found that its dynamic critical properties can be characterized by its damping term alone.

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