Extension of the chiral low-density theorem

We show how the linear "low-density theorem" of Drukarev and Levin can be e xtended to arbitrary positive integer power of the baryon density rho. The nth coefficient in the McLaurin expansion of the fermion condensate's rho d ependence is the connected n-nucleon Sigma term matrix element. We calculat e the O(rho(2)) coefficient in lowest-order perturbative approximation to t he linear sigma model and then show how this and other terms can be iterate d to arbitrarily high order. Convergence radius of the result is discussed. [S0556-2813(99)06905-8].