Gauge coupling unification in the exceptional supersymmetric Standard Model

We consider the renormalisation group flow of gauge couplings within the so-called exceptional supersymmetric Standard Model (E6SSM) based on the low-energy matter content of 27-dimensional representations of the gauge group E6, together with two additional non-Higgs doublets. The two-loop beta functions are computed, and the threshold corrections are studied in the E6SSM. Our results show that gauge coupling unification in the E6SSM can be achieved for phenomenologically acceptable values of α3(MZ), consistent with the central measured low-energy value, unlike in the minimal supersymmetric Standard Model (MSSM) which, ignoring the effects of high energy threshold corrections, requires significantly higher values of α3(MZ), well above the experimentally measured central value.