Marginal Flows between Mirror Pairs of Landau-Ginzburg String Vacua: Thickening Moduli Space via c=0 Theories

A recently introduced method for constructing marginal singular flows between distinct Landau--Ginzburg theories at fixed central charge is reviewed. The flows are constructed in an enlarged moduli space obtained by adding theories with zero central charge. This mechanism is used to construct flows between mirror pairs of string vacua described by N$=$2 superconformal Landau--Ginzburg fixed points. In contrast to previous methods this new construction of mirror theories does not depend on particular symmetries of the original theory. (Based in part on a talk presented at the Trieste Summer Workshop on Superstrings and Related Topics, July 1992)