Density dependent relativistic hadron theory for hadron matter with   inclusion of pentaquark $\Theta^+$
  The density dependent relativistic hadron field theory(DDRH) is extended to inclusions of pentaquark $\Theta^+$. We investigate In-medium properties of $\Theta^+$ and nucleons. As well as the neutron and proton,the effective $\Theta^+$ mass decreases as the baryon density increases,and remains larger than nucleons'. The effective mass of $\Theta^+$ is calculated,$M^*_{\Theta^+}\simeq0.71M_{\Theta^+}$ at normal nuclear density with the fraction of $\Theta^+$ 0.2. The effective masses of all baryon increase with the increasing fraction of $\Theta^+$. The binding energy is also studied. We find the binding energy is much larger than it in nuclear matter without $\Theta^+$,and then discuss the stability of the system with conclusions of pentaquark $\Theta^+$. It is shown that the system becomes bounder added small fraction of $\Theta^+$. Finally we discuss the condition when the system is the most stable and calculate the minimum of binding energy and the fractions of all baryons as functions of baryon density. 
Xi-Guo Lee and Yuan Gao