Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Deriving the gravitational field equation and horizon entropy for
  arbitrary diffeomorphism-invariant gravity from spacetime solid   Motivated by the analogy between the spacetime and the solid with
inhomogeneous elasticity modulus, we present an alternative method to obtain
the field equation of any diffeomorphism-invariant gravity, by extremizing the
constructed entropy function of the displacement vector field of spacetime
solid. In general stationary spacetimes, we show that the Wald entropy of
horizon arises from the on-shell entropy function of spacetime solid.

36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th