DIMENSIONAL EXPANSION FOR THE ISING LIMIT OF QUANTUM-FIELD THEORY

A recently proposed technique, called dimensional expansion, uses the space-time dimension D as an expansion parameter to extract nonperturbative results in quantum field theory. Here we apply dimensional-expansion methods to examine the Ising limit of a self-interacting scalar field theory. We compute the first few coefficients in the dimensional expansion of gamma2n, the renormalized 2n-point Green's function at zero momentum, for n = 2, 3, 4, and 5. Because the exact results for gamma2n are known at D = 1 we can compare the predictions of the dimensional expansion at this value of D. We find typical accuracies of less than 5%. The radius of convergence of the dimensional expansion for gamma2n appears to be 2n/(n - 1). As a function of the space-time dimension D, gamma2n appears to rise monotonically with increasing D and we conjecture that it becomes infinite at D = 2n/(n - 1). We presume that for values of D greater than this critical value gamma2n vanishes identically because the corresponding phi2n scalar quantum field theory is free for D > 2n/(n - 1).