Searching for scalar gravitational interactions in current and future
  cosmological data
  Modified gravity theories often contain a scalar field of gravitational
strength which interacts with matter. We examine constraints on the range and
the coupling strength of a scalar gravitational degree of freedom using a
subset of current data that can be safely analyzed within the linear
perturbation theory. Using a model-independent implementation of scalar-tensor
theories in MGCAMB in terms of two functions of the scale factor describing the
mass and the coupling of the scalar degree of freedom, we derive constraints on
the $f(R)$, generalized chameleon, Symmetron and Dilaton models. Since most of
the large scale structure data available today is from relatively low
redshifts, only a limited range of observed scales is in the linear regime,
leading to relatively weak constraints. We then perform a forecast for a future
large scale structure survey, such as Large Synoptic Survey Telescope (LSST),
which will map a significant volume at higher redshifts, and show that it will
produce much stronger constraints on scalar interactions in specific models. We
also perform a principal component analysis and find that future surveys should
be able to provide tight constraints on several eigenmodes of the scalar mass
evolution.
