Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Radiation driven instability of rapidly rotating relativistic stars:
  criterion and evolution equations via multipolar expansion of gravitational
  waves   I suggest a novel approach for deriving evolution equations for rapidly
rotating relativistic stars affected by radiation-driven
Chandrasekhar-Friedman-Schutz (CFS) instability. This approach is based on the
multipolar expansion of gravitational wave emission and appeals to the global
physical properties of the star (energy, angular momentum, and thermal state),
but not to canonical energy and angular momentum, which is traditional. It
leads to simple derivation of the CFS instability criterion for normal modes
and the evolution equations for a star, affected by this instability. The
approach also gives a precise form to simple explanation of the CFS
instability: it occurs when two conditions met: (a) gravitational wave emission
removes angular momentum from the rotating star (thus releasing the rotation
energy) and (b) gravitational waves carry less energy, than the released amount
of the rotation energy. Results are illustrated by r-mode instability in slowly
rotating Newtonian stars. In resulting evolution equations emission of
gravitational waves directly affects the spin frequency, being in line with the
arguments by Levin & Ushomirsky (2001), but in contrast to widely accepted
equations by Lindblom et al. (1998); Ho & Lai (2000), there effective spin
frequency decrease is coupled with dissipation of unstable mode. This problem,
initially stressed by Levin & Ushomirsky (2001), is shown to be superficial,
and arises as a result of definition of the effective spin frequency by
Lindblom et al. (1998); Ho & Lai (2000). Namely, it is shown, that if this
definition is taken into account properly, the evolution equations coincide
with obtained here in the leading order in mode amplitude. I also argue that
the next-to-leading order terms in evolution equations (which differ for Owen
et al. 1998 and Ho & Lai 2000) require clarification and thus it would be more
self-consistent to omit them.

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The categories of this paper are: cond-mat
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The categories of this paper are: nlin
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The categories of this paper are: alg-geom
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: acc-phys
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The categories of this paper are: cs
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The categories of this paper are: hep-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: solv-int
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-ex