Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin susceptibility and fluctuation corrections in the BCS-BEC crossover
  regime of an ultracold Fermi gas   We investigate magnetic properties and effects of pairing fluctuations in the
BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover
regime of an ultracold Fermi gas. Recently, Liu and Hu, and Parish, pointed out
that the strong-coupling theory developed by Nozi\`eres and Schmitt-Rink (NSR),
which has been extensively used to successfully clarify various physical
properties of cold Fermi gases, unphysically gives negative spin susceptibility
in the BCS-BEC crossover region. The same problem is found to also exist in the
ordinary non-self-consistent T-matrix approximation. In this paper, we clarify
that this serious problem comes from incomplete treatment in term of pseudogap
phenomena originating from strong pairing fluctuations, as well as effects of
spin fluctuations on the spin susceptibility. Including these two key issues,
we construct an extended T-matrix theory which can overcome this problem. The
resulting positive spin susceptibility agrees well with the recent experiment
on a 6Li Fermi gas done by Sanner and co-workers. We also apply our theory to a
polarized Fermi gas to examine the superfluid phase transition temperature Tc,
as a function of the polarization rate. Since the spin susceptibility is an
important physical quantity, especially in singlet Fermi superfluids, our
results would be useful in considering how singlet pairs appear above and below
Tc in the BCS-BEC crossover regime of cold Fermi gases.

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The categories of this paper are: q-bio
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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: nucl-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: astro-ph
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The categories of this paper are: adap-org
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The categories of this paper are: hep-ph
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The categories of this paper are: eess
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The categories of this paper are: physics
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The categories of this paper are: plasm-ph
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The categories of this paper are: math
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The categories of this paper are: stat
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The categories of this paper are: supr-con
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The categories of this paper are: q-alg