  The morphological properties of large scale structure of the Universe can be
fully described by four Minkowski functionals (MFs), which provide important
complementary information to other statistical observables such as the widely
used 2-point statistics in configuration and Fourier spaces. In this work, for
the first time, we present the differences in the morphology of large scale
structure caused by modifications to general relativity (to address the cosmic
acceleration problem), by measuring the MFs from N-body simulations of modified
gravity and general relativity. We find strong statistical power when using the
MFs to constrain modified theories of gravity: with a galaxy survey that has
survey volume $\sim 0.125 (h^{-1}$Gpc$)^3$ and galaxy number density $\sim 1 /
(h^{-1}$Mpc$)^{3}$, the two normal-branch DGP models and the F5 $f(R)$ model
that we simulated can be discriminated from $\Lambda$CDM at a significance
level >~ 5$\sigma$ with an individual MF measurement. Therefore, the MF of
large scale structure is potentially a powerful probe of gravity, and its
application to real data deserves active explorations.
