Viscous Ricci Dark Energy
  We investigate the viscous Ricci dark energy (RDE) model by assuming that
there is bulk viscosity in the linear barotropic fluid and the RDE. In the RDE
model without bulk viscosity, the universe is younger than some old objects at
some redshifts. Since the age of the universe should be longer than any objects
in the universe, the RDE model suffers the age problem, especially when we
consider the object APM 08279+5255 at $z=3.91$, whose age is $t = 2.1$ Gyr. In
this letter, we find that once the viscosity is taken into account, this age
problem is alleviated.
