The rationality problem for multinorm one tori

In this paper, we study the rationality problem for multinorm one tori, a natural generalization of norm one tori. We give a necessary and sufficient condition for the multinorm one tori to be stably rational and retract rational in the case that split over finite Galois extensions with nilpotent Galois groups. This generalizes the result of Endo in 2011 on the rationality problem for norm one tori. To accomplish it, we develop the technique of Endo in 2001, and construct some reduction methods for an investigation of the rationality problem for arbitrary multinorm one tori.