Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Energy of a point-like neutron in an external electromagnetic field   A point-like neutron in an external electromagnetic field experiences a shift
in energy that mimicks the effect of an actual structural deformation of an
extended neutron, i.e., a proper polarizability. In order to be able to
differentiate between the former and the latter, a Foldy-Wouthuysen
transformation is constructed which yields the energy shift of a point-like
neutron quadratic in the external field in a derivative expansion, generalizing
a long-known result for the dipole electric polarizability due to Foldy. The
ten leading Foldy contributions to the energy are determined for a
zero-momentum neutron. In addition, eliminating the momentum operator in favor
of the velocity operator, analogous results are derived for a zero-velocity
neutron. In this case, operator ordering ambiguities are encountered that
permit only a determination of eight of the ten Foldy terms.

27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
2
The categories of this paper are: math