Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Instabilities and the null energy condition   We show that violation of the null energy condition implies instability in a
broad class of models, including classical gauge theories with scalar and
fermionic matter as well as any perfect fluid. When applied to the dark energy,
our results imply that $w = p / \rho$ is unlikely to be less than -1.

30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph