  Chiral perturbation theory is nowadays a well-established approach to
incorporate the chiral constraints from QCD. Nevertheless, for systems
involving one baryon, the power counting which dictates the chiral order of
observables is not as simple and consensual as in the purely mesonic case. The
heavy baryon approach, which relies on a non-relativistic expansion around the
limit of infinitely heavy baryon, recovers the usual power counting but
destroys some analytic properties of the scattering amplitude. Some years ago,
Becher and Leutwyler proposed a Lorentz-invariant formulation of chiral
perturbation theory that maintains the required analytic properties, but at the
expense of a less intuitive power counting.
  Aware of the shortcomings of the heavy baryon formalism, the S\~ao Paulo
group derived the two-pion exchange component of the nucleon-nucleon potential
in line with the works of Becher and Leutwyler. A striking result was that the
long distance properties of the potential is determined by the specific low
energy region of the pion-nucleon scattering amplitude where the heavy baryon
expansion fails. In this talk I will discuss the origin of such failure and how
it reflects in the asymptotics of the nucleon-nucleon interaction. Some results
for phase shifts and deuteron properties will be shown, followed by a
comparison with the heavy baryon predictions.
