The $R_{\mathrm{h}}=ct$ universe and quintessence
  Over the last few years the $R_{\mathrm{h}}=ct$ universe has received a lot of attention, particularly when observational evidence seems to favor this over the standard $\Lambda$ cold dark matter ($\Lambda CDM$) universe. Like the $\Lambda CDM$, the $R_{\mathrm{h}}=ct$ universe is based on a Friedmann-Robertson-Walker (FRW) cosmology where the total energy density $\rho$ and pressure $p$ of the cosmic fluid contain a dark energy component besides the usual (dark and baryonic) matter and radiation components. However unlike the $\Lambda CDM$ this model has the simple equation of state (EOS) $\rho + 3p = 0$, i.e., its total active gravitational mass vanishes, which would therefore exclude a cosmological constant as the source of its dark energy component. Faced with this issue, in this paper we examine various possible sources for the dark energy component of the $R_{\mathrm{h}}=ct$ universe and show that quintessence which has been used in other various dynamical dark energy models could also be a possible source in this case. 
Joseph Sultana
astro-ph.CO gr-qc