Viscous cosmologies with variable $G$ and $\Lambda$ in $R^2$ gravity
  We study evolution of a flat Friedmann-Robertson Walker universe filled with
a bulk viscous cosmological fluid in a higher derivative theory of gravity in
the presence of time varying gravitational and cosmological constant.
Cosmological models admitting both power-law and exponential expansions are
explored here in the presence of imperfect fluid described by full Israel and
Stewart theory. We note some new and interesting cosmological solutions
relevant for model building including present accelerating phase. In the case
of power law, it is found that gravitational constant increases as the time
evolves for a positive cosmological constant whereas it decreases for a
negative cosmological constant. The evolution of temperature of a viscous
universe is also determined.
