Limits on the Gravity Wave Background From Microlensed Quasars

The paper previously submitted under this title is incorrect in that it drastically overestimates the cumulative deflection due to a gravitational wave (GW) background. Avi Loeb gives a simple argument that there can be no $(D\omega {)}^{1\mathrm{/}2}$ enhancement: since the problem is linear in $h$, one can decompose the GWs into plane waves and for each of these there is no enhancement.