# Large Scale Structure as a Probe of Gravitational Slip

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Many modified gravity schemes predict a non-zero difference (gravitational slip\'\') between the Newtonian and longitudinal perturbed metric potentials. Such a slip would affect the growth of large scale structure without altering the expansion history of the universe. We quantify the slip with a new parameter varpi, show the effect of non-zero varpi on the growth of cosmic overdensities, and constrain its value using CMB and weak lensing data.