  By relaxing the conventional assumption of a purely gravitational interaction
between dark energy and dark matter, substantial alterations to the growth of
cosmological structure can occur. In this work we focus on the homogeneous
transfer of energy from a decaying form of dark energy. We present simple
analytic solutions to the modified growth rates of matter fluctuations in these
models, and demonstrate that neglecting physics within the dark sector may
induce a significant bias in the inferred growth rate, potentially offering a
false signature of modified gravity.
