Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Resummation of fermionic in-medium ladder diagrams to all orders   A system of fermions with a short-range interaction proportional to the
scattering length $a$ is studied at finite density. At any order $a^n$, we
evaluate the complete contributions to the energy per particle $\bar E(k_f)$
arising from combined (multiple) particle-particle and hole-hole rescatterings
in the medium. This novel result is achieved by simply decomposing the
particle-hole propagator into the vacuum propagator plus a medium-insertion and
correcting for certain symmetry factors in the $(n-1)$-th power of the
in-medium loop. Known results for the low-density expansion up to and including
order $a^4$ are accurately reproduced. The emerging series in $a k_f$ can be
summed to all orders in the form of a double-integral over an arctangent
function. In that representation the unitary limit $a\to \infty$ can be taken
and one obtains the value $\xi= 0.5067$ for the universal Bertsch parameter. We
discuss also applications to the equation of state of neutron matter at low
densities and mention further extensions of the resummation method.

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The categories of this paper are: eess
10
The categories of this paper are: q-bio
13
The categories of this paper are: quant-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
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The categories of this paper are: nlin
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The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: mtrl-th