Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Non-perturbative calculation of the two-loop Lamb shift in Li-like ions   A calculation valid to all orders in the nuclear-strength parameter is
presented for the two-loop Lamb shift, notably for the two-loop self-energy
correction, to the 2p-2s transition energies in heavy Li-like ions. The
calculation removes the largest theoretical uncertainty for these transitions
and yields the first experimental identification of two-loop QED effects in the
region of the strong binding field.

5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio