Quantum properties of the heterotic five-brane

We find that the conjectured heterotic SO(32) five-brane sigma model develops necessarily k-anomalies, and we investigate their form. We show that these anomalies can be absorbed by modifications of the superspace constraints, that satisfy automatically the modified Bianchi-identity dH7=X8 of N=1, D=10 supergravity. The k-anomalies induce in particular a quantum deformation of the torsion constraint Tαβa=2γαβa.