Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nucleon form factors in dispersively improved Chiral Effective Field
  Theory II: Electromagnetic form factors   We study the nucleon electromagnetic form factors (EM FFs) using a recently
developed method combining Chiral Effective Field Theory ($\chi$EFT) and
dispersion analysis. The spectral functions on the two-pion cut at $t > 4
M_\pi^2$ are constructed using the elastic unitarity relation and an $N/D$
representation. $\chi$EFT is used to calculate the real functions $J_\pm^1 (t)
= f_\pm^1(t)/F_\pi(t)$ (ratios of the complex $\pi\pi \rightarrow N \bar N$
partial-wave amplitudes and the timelike pion FF), which are free of $\pi\pi$
rescattering. Rescattering effects are included through the empirical timelike
pion FF $|F_\pi(t)|^2$. The method allows us to compute the isovector EM
spectral functions up to $t \sim 1$ GeV$^2$ with controlled accuracy (LO, NLO,
and partial N2LO). With the spectral functions we calculate the isovector
nucleon EM FFs and their derivatives at $t = 0$ (EM radii, moments) using
subtracted dispersion relations. We predict the values of higher FF derivatives
with minimal uncertainties and explain their collective behavior. We estimate
the individual proton and neutron FFs by adding an empirical parametrization of
the isoscalar sector. Excellent agreement with the present low-$Q^2$ FF data is
achieved up to $\sim$0.5 GeV$^2$ for $G_E$, and up to $\sim$0.2 GeV$^2$ for
$G_M$. Our results can be used to guide the analysis of low-$Q^2$ elastic
scattering data and the extraction of the proton charge radius.

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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an
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The categories of this paper are: bayes-an
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The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: cs
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The categories of this paper are: hep-ex
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: q-fin
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio