Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Waves and instabilities in an anisotropic universe   The excitation of low frequency plasma waves in an expanding anisotropic
cosmological model which contains a magnetic field frozen into the matter and
pointing in the longitudinal direction is discussed. Using the exact equations
governing finite-amplitude wave propagation in hydromagnetic media within the
framework of general theory of relativity, we show that a spectrum of
magnetized sound waves will be excited and form large scale ``\textit{damped
oscillations}'' on the expanding universe. The characteristic frequency of the
excited waves is slightly shifted away from the sound frequency and the shift
depends on the strength of the primordial magnetic field. This magnetic field
dependent shift may have an effect on the acoustic peaks of the CMB

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The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
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The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph