Varied perturbation theory for the dispersion dip in the two-dimensional Heisenberg quantum antiferromagnet Götz S. Uhrig and Kingshuk Majumdar Eur. Phys. J. B, 86 6 (2013) 282 Published online: 19 June 2013 DOI: 10.1140/epjb/e2013-40159-3