Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Universality of entropy principle for a general diffeomorphism-covariant
  purely gravitational theory   Thermodynamics plays an important role in gravitational theories. It is a
principle independent of the gravitational dynamics, and there is still no
rigorous proof to show that it is consistent with the dynamical principle. We
consider a self-gravitating perfect fluid system in a general
diffeomorphism-covariant purely gravitational theory. Based on the Noether
charge method proposed by Iyer and Wald, considering static off/on-shell
variational configurations which satisfy the gravitational constraint equation,
we rigorously prove that the extrema of the total entropy of perfect fluid
inside a compact region for fixed total particle number demands that the static
configuration is an on-shell solution after we introduce some appropriate
boundary conditions, i.e., it also satisfies the spatial gravitational
equations. This means that the entropy principle of the fluid stores the same
information as the gravitational equation in a static configuration. Our proof
is universal and holds for any diffeomorphism-covariant purely gravitational
theories, such as Einstein gravity, f(R) gravity, Lovelock gravity,
f(Gauss-Bonnet) gravity and Einstein-Weyl gravity. Our result shows the
consistency between the ordinary thermodynamics and the gravitational dynamics.

24
The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ