Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Model independent properties of two-photon exchange in elastic electron
  proton scattering   We derive from first principles, as the C-invariance of the electromagnetic
interaction and the crossing symmetry, the general properties of two-photon
exchange in electron-proton elastic scattering. We show that the presence of
this mechanism destroys the linearity of the Rosenbluth separation.

27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
4
The categories of this paper are: cond-mat
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The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio