Fermions in a Walecka-type cosmology
  A simplified Walecka-type model is investigated in a cosmological scenario. The model includes fermionic, scalar and vector fields as sources. It is shown that their interactions, taking place in a Robertson-Walker metric, could be responsible for the transition of accelerated-decelerated periods in the early universe and a current accelerated regime. It is also discussed the role of the fermionic field as the promoter of the accelerated regimes in the early and the late stages of the universe. 
Marlos O. Ribas, Pedro Zambianchi Jr., Fernando P. Devecchi and   Gilberto M. Kremer
gr-qc astro-ph.CO