Rank 48 gauge group in heterotic string

Andrea Gregori

Published 2000-10-11, updated 2001-10-22Version 2

We discuss the existence of a non-perturbative gauge sector that can raise the rank of the gauge group of the N_4=2 heterotic string up to 48. These gauge bosons, that don't exist in six dimensions, co-exist with those originating from small instantons shrinking to zero size.