Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Variations of Infinite Derivative Modified Gravity   We consider nonlocal modified Einstein gravity without matter, where nonlocal
term has the form $P(R) F(\Box) Q(R)$. For this model, in this paper we give
the derivation of the equations of motion in detail. This is not an easy task
and presented derivation should be useful to a researcher who wants to
investigate nonlocal gravity. Also, we present the second variation of the
related Einstein-Hilbert modified action and basics of gravity perturbations.

19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org