Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Maxwell electrodynamics modified by CPT-even and Lorentz-violating
  dimension-6 higher-derivative terms   In this paper, we investigate an electrodynamics in which the physical modes
are coupled to a Lorentz-violating (LV) background by means of a
higher-derivative term. We analyze the modes associated with the dispersion
relations (DRs) obtained from the poles of the propagator. More specifically,
we study Maxwell's electrodynamics modified by a LV operator of mass dimension
6. The modification has the form
${D_{\beta\alpha}}\partial_{\sigma}F^{\sigma\beta}\partial_{\lambda}
F^{\lambda\alpha}$, i.e., it possesses two additional derivatives coupled to a
\textit{CPT}-even tensor $D_{\beta\alpha}$ that plays the role of the fixed
background. We first evaluate the propagator and obtain the dispersion
relations of the theory. By doing so, we analyze some configurations of the
fixed background and search for sectors where the energy is well-defined and
causality is assured. A brief analysis of unitarity is included for particular
configurations. Afterwards, we perform the same kind of analysis for a more
general dimension-6 model. We conclude that the modes of both Lagrange
densities are possibly plagued by physical problems, including causality and
unitarity violation, and that signal propagation may become physically
meaningful only in the high-momentum regime.

4
The categories of this paper are: cond-mat
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
25
The categories of this paper are: patt-sol
29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
28
The categories of this paper are: alg-geom
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org