Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonlinear vacuum electrodynamics and spontaneous breaking of Lorentz
  symmetry   We study nonlinear vacuum electrodynamics in a first-order formulation
proposed by Pleba\'nski. By applying a Dirac constraint analysis, we derive an
effective Hamiltonian, together with the equations of motion. We show that
there exists a large class of potentials for which the effective Hamiltonian is
bounded from below, while at the same time possessing stationary points in
which the field strength acquires a nonzero vacuum expectation value. The
associated spontaneous breaking of Lorentz symmetry can in principle be
detected by coupling the model to a suitable external current, or to gravity.
We show that the possible vacua can be classified in four classes. We study
some of their properties, using explicit examples for illustration.

21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc