A New Tensor Norm That Preserves Unconditional Bases in Banach Spaces

Abstract: Let $\alpha$ be a tensor norm on the class of all algebaic tensor products of Banach spaces $E\otimes F$. We say that $\alpha$ preserves unconditionality if the completion $E\otimes_{\alpha} F$ admits an unconditional basis for every pair of Banach spaces $E$ and $F$ that have unconditional bases. It is well known that none of Grothendieck's 14 tensor norms satisfies this unconditionality condition. Moreover, the exsistence of a tensor norm $\alpha$ preserving unconditionality remains an open question. In this paper, we construct, for every pair of Banach spaces $E$ and $F$ with unconditional bases a new tensor norm $\alpha$ that preserves unconditionality.