Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Magnetic Structure of Light Nuclei from Lattice QCD   Lattice QCD with background magnetic fields is used to calculate the magnetic
moments and magnetic polarizabilities of the nucleons and of light nuclei with
$A\le4$, along with the cross-section for the $M1$ transition $np\rightarrow
d\gamma$, at the flavor SU(3)-symmetric point where the pion mass is $m_\pi\sim
806$ MeV. These magnetic properties are extracted from nucleon and nuclear
energies in six uniform magnetic fields of varying strengths. The magnetic
moments are presented in a recent Letter. For the charged states, the
extraction of the polarizability requires careful treatment of Landau levels,
which enter non-trivially in the method that is employed. The nucleon
polarizabilities are found to be of similar magnitude to their physical values,
with $\beta_p=5.22(+0.66/-0.45)(0.23) \times 10^{-4}$ fm$^3$ and
$\beta_n=1.253(+0.056/-0.067)(0.055) \times 10^{-4}$ fm$^3$, exhibiting a
significant isovector component. The dineutron is bound at these heavy quark
masses and its magnetic polarizability, $\beta_{nn}=1.872(+0.121/-0.113)(0.082)
\times 10^{-4}$ fm$^3$ differs significantly from twice that of the neutron. A
linear combination of deuteron scalar and tensor polarizabilities is determined
by the energies of the $j_z=\pm 1$ deuteron states, and is found to be
$\beta_{d,\pm 1}=4.4(+1.6/-1.5)(0.2) \times 10^{-4}$ fm$^3$. The magnetic
polarizabilities of the three-nucleon and four-nucleon systems are found to be
positive and similar in size to those of the proton, $\beta_{^{3}\rm
He}=5.4(+2.2/-2.1)(0.2) \times 10^{-4}$ fm$^3$, $\beta_{^{3}\rm
H}=2.6(1.7)(0.1) \times 10^{-4}$ fm$^3$, $\beta_{^{4}\rm
He}=3.4(+2.0/-1.9)(0.2) \times 10^{-4}$ fm$^3$. Mixing between the $j_z=0$
deuteron state and the spin-singlet $np$ state induced by the background
magnetic field is used to extract the short-distance two-nucleon counterterm,
${\bar L}_1$, of the pionless effective theory for $NN$ systems (equivalent to
the meson-exchange current contribution in nuclear potential models), that
dictates the cross-section for the $np\to d\gamma$ process near threshold.
Combined with previous determinations of NN scattering parameters, this enables
an ab initio determination of the threshold cross-section at these unphysical
masses.

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The categories of this paper are: comp-gas
2
The categories of this paper are: math
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-th
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: nlin
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The categories of this paper are: cs
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The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: astro-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: q-fin