Witten diagrams in momentum space and one graviton exchange between scalars in Weyl invariant unimodular gravity

We tackle head on the computation of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>s</a:mi></a:math>-channel Witten diagram in momentum space corresponding to the exchange of a graviton between minimally coupled scalars in Weyl invariant unimodular gravity. By means of a lengthy calculation, we show first that the value of the diagram in question is the same as in general relativity and, then, we obtain a compact expression for it in terms of the Mandelstam variables.