Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Relativistic calculations of the non-resonant two-photon ionization of
  neutral atoms   The non-resonant two-photon one-electron ionization of neutral atoms is
studied theoretically in the framework of relativistic second-order
perturbation theory and independent particle approximation. In particular, the
importance of relativistic and screening effects in the total two-photon
ionization cross section is investigated. Detailed computations have been
carried out for the K-shell ionization of neutral Ne, Ge, Xe, and U atoms. The
relativistic effects significantly decrease the total cross section, for the
case of U, for example, they reduce the total cross section by a factor of two.
Moreover, we have found that the account for the screening effects of the
remaining electrons leads to occurrence of an unexpected minimum in the total
cross section at the total photon energies equal to the ionization threshold,
for the case of Ne, for example, the cross section drops there by a factor of
three.

30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
9
The categories of this paper are: nlin
5
The categories of this paper are: gr-qc