Chiral dynamics and nuclear matter

We calculate the equation of state of isospin-symmetric nuclear matter in the, three-loop approximation of chiral perturbation theory. The contributions to the energy per particle (E) over bar (k(f)) from one- and two-pion exchange diagrams are ordered in powers of the Fermi momentum kf (modulo functions of k(f)/m(pi)). It is demonstrated that, already at order O(k(f)(4)), two-pion exchange produces realistic nuclear binding. The underlying saturation mechanism is surprisingly simple (in the chiral limit), namely the combination of an attractive k(f)(3)-term and a repulsive k(f)(4)-term. The empirical saturation point and the nuclear compressibility K similar or equal to 250 MeV are well reproduced at order O(k(f)(5)) with a momentum cut-off of Lambda similar or equal to 0.65 GeV which parameterizes short-range dynamics. No further short-distance terms are required in our calculation of nuclear matter. In the same framework we calculate the density-dependent asymmetry energy and find A(0) similar or equal to 34 MeV at the saturation point, in good agreement with the empirical value. The pure neutron matter equation of state is also in fair qualitative agreement with sophisticated many-body calculations and a resummation result of effective field theory, but only for low neutron densities rho (n) < 0.25 fm(-3). (C) 2002 Elsevier Science B.V. All rights reserved.