Quark degrees of freedom in nuclear matter

The microscopic theory of Nuclear Matter has been approached along the years by different many-body methods and different nucleon-nucleon (NN) interactions. The realistic NN interactions can be classified mainly into two categories. One relies on the meson-nucleon coupling scheme, within relativistic or non-relativistic framework. The so-called chiral interactions are based on the assumption that, once the pion exchange contribution has been explicitly isolated, it is possible to expand the NN interaction in a series of point interaction terms which respect the underlying QCD chiral symmetry. In both schemes three-body (TBF) or higher forces can be constructed, which can have different degrees of phenomenological character. The TBF are essential to get the Nuclear Matter saturation point close to the phenomenological one. However the QCD quark degrees of freedom are not explicitly introduced. It will be shown that a realistic NN interaction that is constructed from the quark degrees of freedom can produce the correct saturation point without the need of TBF. The corresponding Equation of State is compatible with all the phenomenological constraints, including the Neutron Star maximum mass limit. Taking this result literally, one can say that quarks have been revealed in Nuclear Matter. Another conclusion is that the effect of TBF is model dependent.