text: In the \(d=4\) case, we may see that this Green-Schwarz mechanism makes the previously anomalous \(U(1) a\) gauge boson massive and the "Stckelberg" mass is just an order of magnitude or so lower than the string scale (which they therefore assume to be \(M s\approx 20\TeV\)). This is normally viewed as an extremely high energy scale which is why these possibilities don't enter the conventional quantum field theoretical models.