Spreading of gauge coupling constants in minimal LR models

Minimal left-right (LR) models are often inconsistent with gauge unification at the Planck scale, as they imply too large a Weinberg angle. In (E6) superstring-inspired models true gauge unification is not required, and the absence of unification of coupling constants might be an indication of non-zero (string) renormalization effects. Here we perform a quantitative analysis of the necessary spreading of the gauge coupling constants in order to accommodate a realistic value of the Weinberg angle in minimal LR models motivated by the string. (orig.)