Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Energy expectation values of a particle in nonstationary fields   We show that the origin of the nonequivalence of Hamiltonians in different
representations is a change of the form of the time-derivative operator at a
time-dependent unitary transformation. This nonequivalence does not lead to an
ambiguity of the energy expectation values of a particle in nonstationary
fields but assigns the basic representation. It has been explicitly or
implicitly supposed in previous investigations that this representation is the
Dirac one. We prove the alternative assertion about the basic role of the
Foldy-Wouthuysen representation. We also derive the general equation for the
energy expectation values in the Dirac representation. As an example, we
consider a spin-1/2 particle with anomalous magnetic and electric dipole
moments in strong time-dependent electromagnetic fields. We apply the obtained
results to a spin-1/2 particle in a plane monochromatic electromagnetic wave
and give an example of the exact Foldy-Wouthuysen transformation in the
nonstationary case.

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The categories of this paper are: adap-org
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess