Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Negative mass hydrodynamics in a Spin-Orbit--Coupled Bose-Einstein
  Condensate   A negative effective mass can be realized in quantum systems by engineering
the dispersion relation. A powerful method is provided by spin-orbit coupling,
which is currently at the center of intense research efforts. Here we measure
an expanding spin-orbit coupled Bose-Einstein condensate whose dispersion
features a region of negative effective mass. We observe a range of dynamical
phenomena, including the breaking of parity and of Galilean covariance,
dynamical instabilities, and self-trapping. The experimental findings are
reproduced by a single-band Gross-Pitaevskii simulation, demonstrating that the
emerging features - shockwaves, soliton trains, self-trapping, etc. - originate
from a modified dispersion. Our work also sheds new light on related phenomena
in optical lattices, where the underlying periodic structure often complicates
their interpretation.

5
The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
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The categories of this paper are: physics
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg