Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vacua and instantons of ghost-free massive gravity   Recently discovered models of ghost-free massive gravity and bigravity are
characterized by a non-trivial potential that gives rise to a rich vacuum
structure. We review maximally symmetric vacua of the de Rham-Gabadadze-Tolley
(dRGT) massive gravity and of the Hassan-Rosen (HR) bigravity, and discuss
their perturbative stability. In particular, we discuss perturbations about
self-accelerating vacua in HR bigravity, and argue that, analogously to what
was found in the case of dRGT gravity, some of them contain strongly coupled
modes. We then show that it is impossible to construct regular instantons
connecting different classically stable vacua of dRGT gravity without violating
energy conservation or the null energy condition.

14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn