Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High Frequency Sound in a Unitary Fermi Gas   We present an experimental and theoretical study of the phonon mode in a
unitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation
spectra at a momentum of approximately half the Fermi momentum, both above and
below the superfluid critical temperature $T_\mathrm{c}$. Below $T_\mathrm{c}$,
the dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by
gradients in the phase of the superfluid order parameter. The temperature
dependence of the BA phonon is consistent with a theoretical model based on the
quasiparticle random phase approximation in which the dominant damping
mechanism is via collisions with thermally excited quasiparticles. As the
temperature is increased above $T_\mathrm{c}$, the phonon evolves into a
strongly damped collisional mode, accompanied by an abrupt increase in spectral
width. Our study reveals strong similarities between sound propagation in the
unitary Fermi gas and liquid helium.

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The categories of this paper are: math
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
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The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
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
23
The categories of this paper are: solv-int
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-th