Chiral symmetry and quantum hadrodynamics

Using the linear sigma model, we study the evolutions of the quark condensate and of the nucleon mass in the nuclear medium. Our formulation of the model allows the inclusion of both pion and scalar-isoscalar degrees of freedom. It guarantees that the low-energy theorems and the constraints of chiral perturbation theory are respected. We show how this formalism incorporates quantum hadrodynamics improved by the pion loop effects.