Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spontaneous solitons in the thermal equilibrium of a
  quasi-one-dimensional Bose gas   Solitons, or non-destructible local disturbances, are important features of
many one-dimensional (1D) nonlinear wave phenomena, from water waves in narrow
canals to light pulses in optical fibers. In ultra-cold gases, they have long
been sought, and were first observed to be generated by phase-imprinting. More
recently, their spontaneous formation in 1D gases was predicted as a result of
the Kibble-Zurek mechanism, rapid evaporative cooling, and dynamical processes
after a quantum quench. Here we show that they actually occur generically in
the thermal equilibrium state of a weakly-interacting elongated Bose gas,
without the need for external forcing or perturbations. This reveals a major
new quality to the experimentally widespread quasicondensate state. It can be
understood via thermal occupation of the famous and somewhat elusive Type II
excitations in the Lieb-Liniger model of a uniform 1D gas.

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The categories of this paper are: quant-ph
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The categories of this paper are: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
2
The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: eess
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: q-fin