Algebraic Theory of Causal Double Products

Abstract

Corresponding to each “rectangular” double product in the form of a formal power series R[h] with coefficients in the tensor product 풯(ℒ)⊙ 풯 (ℒ) with itself of the Itô Hopf algebra, we construct “triangular” elements T[h] of 풯(ℒ) satisfying ΔT[h] = T[h]⁽¹⁾ R[h]T{h]⁽²⁾. In Fock space representations of 풯(ℒ) by iterated quantum stochastic integrals when ℒ is the algebra of Itô differentials of the calculus, these correspond to “causal” double product integrals in a single Fock space.