diff --git a/README.md b/README.md
index ab0f862..7820ab1 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,8 @@ The main target for the week was to implement a simple intensity function for tw
 
 where $Z_{l}^{m}(\Omega,\Phi)=Y_{l}^{m}(\Omega)e^{-i\Phi}$ is a phase-rotated spherical harmonic, $\Omega$ is the solid angle, $\Phi$ is the angle between the production and polarization planes, $P_{\gamma}$ is the polarization magnitude, $[l]$ are the partial wave amplitudes, $m$ is the associated m-projection, $k$ refers to a spin flip ($k=1$) or non-flip ($k=0$) at the nucleon vertex, and $\kappa$ is an overall phase space factor.
 
+The details for this model have been worked out in [10.1103/PhysRevD.100.054017](https://doi.org/10.1103/PhysRevD.100.054017) (2019).
+
 ![](docs/fig/feynman-gluex-two-pseudoscalar.svg)
 
 The amplitude model is implemented in [AmpTools](https://github.com/mashephe/AmpTools) and symbolically in Python using [SymPy](https://docs.sympy.org) with additional tools from [`amptools`](https://ampform.rtfd.io) ([ComPWA Project](https://compwa.github.io)). Dynamics are not yet included (model-indepedent by binning over energy). So we are just comparing linar combinations of spherical harmonics, but the comparison can be extended by investigating final states with a vector meson and/or parametrizing dynamic lineshapes.
diff --git a/docs/index.md b/docs/index.md
index 10d6fe3..7ae28e1 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -17,15 +17,15 @@ I(\Omega,\Phi) = 2\kappa\sum_{k}\left(
 
 ```{include} ../README.md
 :start-line: 10
-:end-line: 12
+:end-line: 14
 ```
 
 :::{figure} fig/feynman-gluex-two-pseudoscalar.svg
 :::
 
 ```{include} ../README.md
-:start-line: 14
-:end-line: 15
+:start-line: 16
+:end-line: 17
 ```
 
 :::{figure} fig/feynman-gluex-vector-meson.svg