Temporary HW

Problem 1: Ginzburg criterion in arbitrary spatial dimension and upper critical dimension

The general solution for the correlation function in arbitrary spatial dimension within the mean-field theory can be written as:

$G(r)\sim {\frac {e^{-}{r/\xi }}{r^{d-2}}}$

assuming that distance $r\gg a$ is much larger than the lattice spacing $a$.