Pade-Borel approximation of the continuum limit of strong coupling   lattice fields: Two dimensional non-linear O(N) sigma model at N>=3
  Based on the strong coupling expansion, we reinvestigate two dimensional O(N) sigma model by the use of Pade-Borel approximants. The conventional strong coupling expansion of the mass square M in momentum space in beta=1/g^2 is inverted to give beta expanded in 1/M. Borel transform of beta with respect to M is carried out and the result is improved as the rational function by Pade method. We find the behavior of Pade-Borel transformed bare coupling at 18th order is consistent for N>=3 with that of continuum scaling to the four-loop perturbation theory. We estimate non-perturbative mass gap at N>=3 and find the agreement with the exact result by Hasenfratz et.al. 
Hirofumi Yamada
hep-lat hep-ph hep-th