Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Order \alpha^4 R_{\infty} corrections to positronium P levels   The order $\alpha^4 R_{\infty}$ corrections to positronium $P$ levels are
found. The calculation is reduced to the ordinary perturbation theory for the
nonrelativistic Schr\"odinger equation. The perturbation operators have the
Breit-type structure and are obtained by calculating on-mass-shell diagrams.
Found energy corrections constitute numerically $\delta E(2 ^1 P_1)=0.06$ MHz,
$\delta E(2 ^3 P_2)=0.08$ MHz, $\delta E(2 ^3 P_1)=0.025$ MHz, $\delta E(2 ^3
P_2)=-0.58$ MHz.

10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc