Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: HFS interval of the $2s$ state of hydrogen-like atoms and a constraint
  on a pseudovector boson with mass below $1\;$keV$/c^2$   A constraint on a long-range spin-dependent interaction
$\alpha^{\prime\prime}({\bf s}_1\cdot{\bf s}_2)\,{\rm e}^{-\lambda r}/r$, which
can be induced by a pseudovector light boson, is presented. We study
theoretical and experimental data on a specific difference $8\times E_{\rm
hfs}(2s)-E_{\rm hfs}(1s)$ for light two-body atoms. The spin-dependent coupling
constant $\alpha^{\prime\prime}$ of electron-nucleus interaction in hydrogen,
deuterium and helium-3 ion is constrained at the level below a part in
$10^{16}$. The derived constraints are related to the range of masses below
$4\;{\rm keV}/c^2$.

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The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int