Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Equilibrium thermodynamics in modified gravitational theories   We show that it is possible to obtain a picture of equilibrium thermodynamics
on the apparent horizon in the expanding cosmological background for a wide
class of modified gravity theories with the Lagrangian density $f(R, \phi, X)$,
where $R$ is the Ricci scalar and $X$ is the kinetic energy of a scalar field
$\phi$. This comes from a suitable definition of an energy momentum tensor of
the "dark" component that respects to a local energy conservation in the Jordan
frame. In this framework the horizon entropy $S$ corresponding to equilibrium
thermodynamics is equal to a quarter of the horizon area $A$ in units of
gravitational constant $G$, as in Einstein gravity. For a flat cosmological
background with a decreasing Hubble parameter, $S$ globally increases with
time, as it happens for viable $f(R)$ inflation and dark energy models. We also
show that the equilibrium description in terms of the horizon entropy $S$ is
convenient because it takes into account the contribution of both the horizon
entropy $\hat{S}$ in non-equilibrium thermodynamics and an entropy production
term.

26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys