  Transparent media exhibiting anomalous dispersion have been of considerable
interest since Wang, Kuzmich, and Dogariu [Nature {\bf 406}, 277 (2000)] first
observed light propagate with superluminal and negative group velocities
without absorption. Here, we propose an atomic model exhibiting these
properties, based on a generalization of amplification without inversion in a
five-level DIGS system. The system consists of a $\Lambda$ atom prepared as in
standard electromagnetically induced transparency (EIT), with two additional
metastable ground states coupled to the $\Lambda$ atom ground states by two
RF/microwave fields. We consider two configurations by which population is
incoherently pumped into the ground states of the atom. Under appropriate
circumstances, we predict a pair of new gain lines with tunable width,
separation, and height. Between these lines, absorption vanishes but dispersion
is large and anomalous. The system described here is a significant improvement
over other proposals in the anomalous dispersion literature in that it permits
additional coherent control over the spectral properties of the anomalous
region, including a possible $10^4$-fold increase over the group delay observed
by Wang, Kuzmich, and Dogariu.
