removed a sentence to be revised later.
@@ -185,7 +185,7 @@ In doing this, \ccl simultaneously computes the logarithmic growth rate $f(a)$,
\ccl provides functions that return the growth normalized to $D(a=1)=1$ and to $D(a\ll1)\rightarrow a$. It employs an accelerated spline that is linearly spaced in the scale factor to interpolate the growth functions.
-The growth calculations cover flat and curved $\Lambda$CDM, $w$CDM, and $(w_0 + w_a)$CDM cosmologies. However, it should be noted that the above treatment is strictly valid for a Universe containing only dust-like matter components. A scale-independent growth rate is, for example, ill-defined in the presence of massive neutrinos, and attempts to compute the growth rate in cosmologies with massive neutrinos will get an inconsistent result.
+The growth calculations cover flat and curved $\Lambda$CDM, $w$CDM, and $(w_0 + w_a)$CDM cosmologies. However, it should be noted that the above treatment is ill-defined in the presence of massive neutrinos, and attempts to compute the growth rate in cosmologies with massive neutrinos will get an inconsistent result.
Finally, \ccl allows for an alternative `modified gravity' cosmological model defined by a regular curved $(w_0+w_a)$CDM background as well as a user-defined $\Delta f(a)$, such that the true growth rate in this model is given by $f(a)=f_0(a)+\Delta f(a)$, where $f_0(a)$ is the growth rate in the background model. Note that this model is only consistently implemented with regards to the computation of the linear growth factor and growth rates.
All other \ccl functions (including the non-linear power spectrum) will ignore these modifications. This model, and the interpretation of the predictions given by \ccl, should therefore be used with care. A version of the growth code and transfer functions depending on modified gravity parameters is under development.
