Study of Thermodynamic Quantities in Generalized Gravity Theories
  In this work, we have studied the thermodynamic quantities like temperature
of the universe, heat capacity and squared speed of sound in generalized
gravity theories like Brans-Dicke, Ho$\check{\text r}$ava-Lifshitz and $f(R)$
gravities. We have considered the universe filled with dark matter and dark
energy. Also we have considered the equation of state parameters for open,
closed and flat models. We have observed that in all cases the equation of
state behaves like quintessence. The temperature and heat capacity of the
universe are found to decrease with the expansion of the universe in all cases.
In Brans-Dicke and $f(R)$ gravity theories the squared speed of sound is found
to exhibit increasing behavior for open, closed and flat models and in
Ho$\check{\text r}$ava-Lifshitz gravity theory it is found to exhibit
decreasing behavior for open and closed models with the evolution of the
universe. However, for flat universe, the squared speed of sound remains
constant in Ho$\check{\text r}$ava-Lifshitz gravity.
