On the chiral low-density theorem

We show how the linear "low-density theorem" of Drukarev and Levin can be extended to arbitrary positive integer power of the baryon density $\rho$. The n^th coefficient in the McLaurin expansion of the fermion condensate's $\rho$ dependence is the connected n-nucleon sigma term matrix element. We calculate the $O(\rho^2)$ coefficient in lowest-order perturbative approximation to the linear sigma model and then show how this and other terms can be iterated to arbitrarily high order. Convergence radius of the result is discussed.