Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: CPT and Lorentz Symmetry in Hydrogen and Antihydrogen   Possibilities for observing signals of CPT and Lorentz violation in the
spectroscopy of hydrogen and antihydrogen are considered. We show that
transitions between the c and d hyperfine sublevels in the 1S state can exhibit
theoretically detectable effects that would be unsuppressed by powers of the
fine-structure constant. This transition may therefore offer some advantages
over 1S-2S two-photon spectroscopy.

7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an