Two Windows on Acceleration and Gravitation: Dark Energy or New Gravity?
  Small distortions in the observed shapes of distant galaxies, a cosmic shear due to gravitational lensing, can be used to simultaneously determine the distance-redshift relation, r(z), and the density contrast growth factor, g(z). Both of these functions are sensitive probes of the acceleration. Their simultaneous determination allows for a consistency test and provides sensitivity to physics beyond the standard dark energy paradigm. 
L. Knox (UCD), Y.-S. Song (U Chicago) and J.A. Tyson (UCD)