On stability of the three-dimensional fixed point in a model with three   coupling constants from the $\epsilon$ expansion: Three-loop results
  The structure of the renormalization-group flows in a model with three quartic coupling constants is studied within the $\epsilon$-expansion method up to three-loop order. Twofold degeneracy of the eigenvalue exponents for the three-dimensionally stable fixed point is observed and the possibility for powers in $\sqrt{\epsilon}$ to appear in the series is investigated. Reliability and effectiveness of the $\epsilon$-expansion method for the given model is discussed. 
Andrei Mudrov and Konstantin Varnashev