Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Double layers in gravity theories   Gravitational double layers, unlike their classical electromagnetic
counterparts, are thought to be forbidden in gravity theories. It has been
recently shown, however, that they are feasible in, for instance, gravity
theories with a Lagrangian quadratic in the curvature. This is surprising with
many potential consequences and the possibility of new physical behaviours.
While a clear interpretation seems elusive, several lines of research are open.
I present the field equations for double layers, the new physical quantities
arising, and several explicit examples.

28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an