Nuclear matter within a dilatation-invariant parity doublet model: the   role of the tetraquark at nonzero density
  We investigate the role of a scalar tetraquark state for the description of nuclear matter within the parity doublet model in the mirror assignment. In the dilatation-invariant version of the model a nucleon-nucleon interaction term mediated by the lightest scalar tetraquark field naturally emerges. At nonzero density one has, beyond the usual chiral condensate, also a tetraquark condensate. The behavior of both condensates and the restoration of chiral symmetry at high density are studied. It is shown that this additional scalar degree of freedom affects non negligibly the properties of the medium. 
Susanna Gallas, Francesco Giacosa, and Giuseppe Pagliara
hep-ph nucl-th