First-order quantum correction to the ground-state energy density of   two-dimensional hard-sphere Bose atoms
  Divergence exponents of the first-order quantum correction of a two-dimensional hard-sphere Bose atoms are obtained by an effective field theory method. The first-order correction to the ground-state energy density with respect to the zeroth-order is given by   $\cale_1/\cale_0 \sim |D-2|^{-\al}|\ln\gamma|^{-\al'}$, where $D$ is the spatial dimension, and $\gamma$ is the gas parameter ($\gamma=n a^D$). As $D \to 2$, $\al =\al'=1$. We show that the first-order quantum correction of the energy density is not perturbative in low dimensions of $D < 2.2$ regardless of any gas parameter which is much less that 1. 
Sang-Hoon Kim, Mukunda P. Das