Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dispersive evaluation of the second-class amplitude
  $\tau\to\eta\pi\nu_\tau$ in the standard model   We reevaluate the two form factors relevant for the $\eta\pi$ second-class
$\tau$ decay mode, making systematic use of analyticity, unitarity, combined
with updated inputs to the NLO chiral constraints. We focus, in particular, on
the shape of the $\rho$ resonance peak which is a background-free signature of
a second-class current. Its dispersive construction requires the
$\eta\pi\to\pi\pi$ scattering amplitude which we derive from a family of
Khuri-Treiman equations solutions constrained with accurate recent results on
the $\eta\to3\pi$ Dalitz plot.

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The categories of this paper are: cond-mat
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The categories of this paper are: eess
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The categories of this paper are: astro-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: physics
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-alg
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
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The categories of this paper are: bayes-an
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org