On the Geometry of Projective Tensor Products

In this work, we study the volume ratio of the projective tensor products `p ⊗π `q ⊗π `r with 1 ≤ p ≤ q ≤ r ≤ ∞. We obtain asymptotic formulas that are sharp in almost all cases. As a consequence of our estimates, these spaces allow for a nearly Euclidean decomposition of Kašin type whenever 1 ≤ p ≤ q ≤ r ≤ 2 or 1 ≤ p ≤ 2 ≤ r ≤ ∞ and q = 2. Also, from the Bourgain-Milman bound on the volume ratio of Banach spaces in terms of their cotype 2 constant, we obtain information on the cotype of these 3-fold projective tensor products. Our results naturally generalize to k-fold products `np1 ⊗π · · · ⊗π ` n pk with k ∈ N and 1 ≤ p1 ≤ · · · ≤ pk ≤ ∞.