Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: $\boldsymbol{\eta}$-$\boldsymbol{^4{\rm He}}$ interaction from the
  $\boldsymbol{d d \to \eta ^4{\rm He}}$ reaction near threshold   We analyze the data on the total cross sections for the $dd \to \eta{}^4{\rm
He}$ reaction close to threshold and look for possible $\eta ^4 {\rm He}$ bound
states. We develop a framework in which the $\eta ^4{\rm He}$ optical potential
is the key ingredient, rather than parameterizing the scattering matrix, as is
usually done. The strength of this potential, together with some production
parameters, are fitted to the available experimental data. The relationship of
the scattering matrix to the optical potential is established using the
Bethe-Salpeter equation and the $\eta ^4{\rm He}$ loop function incorporates
the range of the interaction given by the experimental $^4 {\rm He}$ density.
However, when we look for poles of the scattering matrix, we get poles in the
bound region, poles in the positive energy region or no poles at all. If we
further restrict the results with constraints from a theoretical model with all
its uncertainties the bound states are not allowed. However, we find a bump
structure in $|T|^2$ of the $\eta ^4{\rm He} \to \eta ^4{\rm He}$ amplitude
below threshold for the remaining solutions.

7
The categories of this paper are: hep-th
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The categories of this paper are: astro-ph
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The categories of this paper are: gr-qc
19
The categories of this paper are: eess
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The categories of this paper are: hep-ex
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph