Published online by Cambridge University Press: 20 November 2018
Inspired by a construction by Bump, Friedberg, and Ginzburg of a two-variable integral representation on  
 $\text{GS}{{\text{p}}_{4}}$  for the product of the standard and spin  
 $L$ -functions, we give two similar multivariate integral representations. The first is a three-variable Rankin-Selberg integral for cusp forms on  
 $\text{PG}{{\text{L}}_{4}}$  representing the product of the  
 $L$ -functions attached to the three fundamental representations of the Langlands  
 $L$ -group  
 $\text{S}{{\text{L}}_{\text{4}}}\left( \text{C} \right)$ . The second integral, which is closely related, is a two-variable Rankin-Selberg integral for cusp forms on  
 $\text{PGU}\left( 2,\,2 \right)$  representing the product of the degree  
 $8$  standard  
 $L$ -function and the degree  
 $6$  exterior square  
 $L$ -function.