Thermodynamic properties of the phi4 lattice field theory near the Ising limit

For a d-dimensional phi4 lattice field theory consisting of N spins with nearest-neighbor interactions, the partition function is transformed for large bare coupling constant lambda into an Ising-like system with additional neighbor interactions. For d=2 a mean field approximation is then used to estimate the difference in critical temperature between the lattice phi4 field theory and its Ising limit (lambda=infinity). Expansions are obtained for the susceptibility and specific heat. The critical exponents are shown to be identical to the Ising exponents