Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Higher order corrections to the hydrogen spectrum from the
  Standard-Model Extension   We have studied the effects of the Standard-Model Extension (SME) on hydrogen
as a realization of new physics effects that incorporate Lorentz and CPT
violation. Specifically, we calculated the SME-induced energy level shifts at
order $\alpha^2$ times the SME parameters. We obtained contributions at this
order both from the non-relativistic effective Hamiltonian for motion of a
spin-1/2 particle in the presence of SME interactions and also from SME
corrections to the propagator for exchange photons. We applied our result to
the $2S-1S$ transition in hydrogen, which has been measured with extremely high
precision. The results obtained in this work give the leading SME corrections
for this transition.

17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
2
The categories of this paper are: math
18
The categories of this paper are: econ
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex