Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ultrarelativistic electron states in a general background
  electromagnetic field   The feasibility of obtaining exact analytical results in the realm of QED in
the presence of a background electromagnetic field is almost exclusively
limited to a few tractable cases, where the Dirac equation in the corresponding
background field can be solved analytically. This circumstance has restricted,
in particular, the theoretical analysis of QED processes in intense laser
fields to within the plane-wave approximation even at those high intensities,
achievable experimentally only by tightly focusing the laser energy in space.
Here, within the Wentzel-Kramers-Brillouin (WKB) or eikonal approximation, we
construct analytically single-particle electron states in the presence of a
background electromagnetic field of general space-time structure in the
realistic assumption that the initial energy of the electron is the largest
dynamical energy scale in the problem. The relatively compact expression of
these states opens, in particular, the possibility of investigating
analytically strong-field QED processes in the presence of spatially focused
laser beams, which is of particular relevance in view of the upcoming
experimental campaigns in this field.

32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org