Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Foldy-Wouthyusen Transformation and Semiclassical Limit for Relativistic
  Particles in Strong External Fields   A general method of the Foldy-Wouthyusen (FW) transformation for relativistic
particles of arbitrary spin in strong external fields has been developed. The
use of the found transformation operator is not restricted by any definite
commutation relations between even and odd operators. The final FW Hamiltonian
can be expanded into a power series in the Planck constant which characterizes
the order of magnitude of quantum corrections. Exact expressions for low-order
terms in the Planck constant can be derived. Finding these expressions allows
to perform a simple transition to the semiclassical approximation which defines
a classical limit of the relativistic quantum mechanics. As an example,
interactions of spin-1/2 and scalar particles with a strong electromagnetic
field have been considered. Quantum and semiclassical equations of motion of
particles and their spins have been deduced. Full agreement between quantum and
classical theories has been established.

0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
17
The categories of this paper are: q-fin
16
The categories of this paper are: stat