Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Horizon thermodynamics in fourth-order gravity   In the framework of horizon thermodynamics, the field equations of Einstein
gravity and some other second-order gravities can be rewritten as the
thermodynamic identity: $dE=TdS-PdV$. However, in order to construct the
horizon thermodynamics in higher-order gravity, we have to simplify the field
equations firstly. In this paper, we study the fourth-order gravity and convert
it to second-order gravity via a so-called " Legendre transformation " at the
cost of introducing two other fields besides the metric field. With this
simplified theory, we implement the conventional procedure in the construction
of the horizon thermodynamics in 3 and 4 dimensional spacetime. We find that
the field equations in the fourth-order gravity can also be written as the
thermodynamic identity. Moreover, we can use this approach to derive the same
black hole mass as that by other methods.

27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th