Gravitational lens time delays and gravitational waves.

Using Fermat’s principle, we analyze the effects of very long wavelength gravitational waves upon the images of a gravitationally lensed quasar. We show that the lens equation in the presence of gravity waves is equivalent to that of a lens with different alignment between source, deflector, and observer in the absence of gravity waves. Contrary to a recent claim, we conclude that measurements of time delays in gravitational lenses cannot serve as a method to detect or constrain a stochastic background of gravitational waves of cosmological wavelengths, because the waveinduced time delay is observationally indistinguishable from an intrinsic time delay due to the lens geometry. PACS numbers: 98.80.-k, 04.80.+z, 95.30.Sf Typeset using REVTEX 1