Variational Resummation of $\epsilon$-Expansions of Critical Exponents   of Nonlinear O(N)-Symmetric $\sigma$-Model in $2+\epsilon$ Dimensions
  We develop a method for extracting accurate critical exponents from perturbation expansions of the O(n)-symmetric nonlinear sigma-model in D=2+ epsilon dimensions. This is possible by considering the epsilon-expansions in this model as strong-coupling expansions of functions of the variable tildevarepsilon = 2(4-D)/(D-2), whose first five weak-coupling expansion coefficients of powers of tildevarepsilon are known from varepsilon-expansions of critical exponents in O(n)-symmetric phi^4-theory in D=4-epsilon dimensions. 
Hagen Kleinert