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 ρ. The nth coefficient in the McLaurin expansion of the fermion condensate’s ρ dependence is the connected n-nucleon sigma term matrix element. We calculate the O(ρ2) 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. PACS numbers: 21.65.+f, 11.30.Rd, 24.85.+p