Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Primordial magnetic fields generated by the non-adiabatic fluctuations
  at pre-recombination era   In the pre-recombination era, cosmological density fluctuations can naturally
generate magnetic fields through Thomson scatterings. In previous studies, only
the magnetic field generation from the initially-adiabatic fluctuations has
been considered. Here we investigate the generation of cosmological magnetic
fields sourced by the primordial non-adiabatic fluctuations based on the
cosmological perturbation theory, using the tight-coupling approximations
between photon and baryon fluids. It is found that the magnetic fields from the
non-adiabatic fluctuations can arise at the first-order expansion of the tight
coupling approximation. This result is in contrast to the case of adiabatic
initial fluctuations, where the magnetic fields can be generated only at the
second-order. In a general case where the primordial density perturbations
contain small non-adiabatic fluctuations on the top of the dominant adiabatic
ones, we show that the leading source of magnetic fields is given by the
second-order coupling of the adiabatic and non-adiabatic fluctuations. We
calculate the power spectrum of the generated magnetic fields when the
non-adiabatic fluctuations have a blue power spectrum, which has been suggested
by recent cosmological observations.

37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
23
The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph
30
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: q-fin