branching index in polymers

A parameter, $g$ , characterizing the effect of long-chain branches on the size of a branched macromolecule in solution and defined as the ratio of the mean-square radius of gyration of a branched molecule, $s b 2$ , to that of an otherwise identical linear molecule, $s l 2$ , with the same relative molecular mass in the same solvent and at the same temperature, i.e. $g = s b 2 s l 2$ .

Source:

Purple Book, p. 51