@HLZ]. Using these, it can be shown that the process $e^+ e^- \to  e^+ e^- G_n$ is driven, at tree-level, by 28 Feynman diagrams. Some representative diagrams are shown in Fig. 1, which are obtained by ‘dressing’ an $s$-channel process $e^+ e^- \to  e^+ e^-$ with graviton radiation. Fig. 1($a$) represents a graviton emission from one of the external electron legs; there will be 4 such diagrams with the graviton emitted from [*each*]{} leg in turn. Fig. 1($b$) represents a graviton emission from the gauge boson propagator. Fig. 1($c$) represents a graviton emission from one vertex; there will be another such with graviton emission from the other vertex. Thus Fig. 1 encompasses 14 diagrams, 7 each with $Z$ and photon exchanges. In addition, there will be another set of 14 diagrams with the $\gamma,Z$ exchange in the $t$-channel, making 28 diagrams in all. This latter set is absent in the case of $e^+ e^- \to  \mu^+ \mu^- G_n$.

=1.3 pt

(90,90)(0,0) (0,20)(30,40) (30,40)(0,60) (30,40)(60,40)[4]{}[3]{} (60,40)(90,20) (90,60)(60,40) (15,50)(45,70)[3]{}[5]{} (45,70)(15,50)[-3]{}[5]{} (0,15)\[l\][$e^-$]{} (0,70)\[l\][$e^+$]{} (45,25)\[c\][$\gamma ,Z$]{} (100,15)\[r\][$e^+$]{} (100,70)\[r\][$e^-$]{} (59,75)\[r\][$G$]{} (45,8)\[c\][$(a)$]{}

(90,90)(0,0) (0,20)(30,40) (30,40)(0,60) (30,40)(60,40)[4]{}[3]{} (60,40)(90,20) (90,60)(60,40) (45,40)(45,70)[3]{}[5]{} (45,70)(45,40)[-3]{}[5]{} (0,15)\[l\][$e^-$]{} (0,70)\[l\][$e^+$]{} (45,25)\[c\][$\gamma ,Z$]{} (100,15)\[r\][$e^+$]{} (100,70)\[r\][$e^-$]{} (45,80)\[c\][$G$]{} (45,8)\[c\][$(b)$]{}

(90,90)(0,0) (0,20)(30,40) (30,40)(0,60) (30,40)(60,40)[4]{}[3]{} (60,40)(90,20) (90,60)(60,40) (60,40)(90,40)[3]{}[5]{} (90,40)(60,40)[-3]{}[5]{} 