Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 3D evolution of magnetic fields in a differentially rotating stellar
  radiative zone   The question of the origin and evolution of magnetic fields in stars
possessing a radiative envelope, like the A-type stars, is still regarded as a
challenge for stellar physics. Those zones are likely to be differentially
rotating, which suggests that strong interactions between differential rotation
and magnetic fields could be at play. We numerically compute the joint
evolution of the magnetic and velocity fields in a 3D spherical shell starting
from an initial profile for the poloidal magnetic field and differential
rotation. The poloidal magnetic field is initially wound-up by the differential
rotation to produce a toroidal field which becomes unstable. In the particular
setup studied here where the differential rotation is dominant, the
magneto-rotational instability is triggered. The growth rate of the instability
depends mainly on the initial rotation rate, while the background state
typically oscillates over a poloidal Alfv\'en time. We thus find that the
axisymmetric magnetic configuration is strongly modified by the instability
only if the ratio between the poloidal Alfv\'en frequency and the rotation rate
is sufficiently small. An enhanced transport of angular momentum is found in
the most unstable cases: the typical time to flatten the rotation profile is
then much faster than the diffusion time scale. We conclude that the
magneto-rotational instability is always favored (over the Tayler instability)
in unstratified spherical shells when an initial poloidal field is sheared by a
sufficiently strong cylindrical differential rotation. A possible application
to the magnetic desert observed among A stars is given. We argue that the
dichotomy between stars exhibiting strong axisymmetric fields (Ap stars) and
those harboring a sub-Gauss magnetism could be linked to the threshold for the
instability.

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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: funct-an
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: hep-th
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The categories of this paper are: econ
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The categories of this paper are: hep-ph
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The categories of this paper are: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci