Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Was The Electromagnetic Spectrum A Blackbody Spectrum In The Early
  Universe?   It is assumed, in general, that the electromagnetic spectrum in the
Primordial Universe was a blackbody spectrum in vacuum. We derive the
electromagnetic spectrum, based on the Fluctuation-Dissipation Theorem that
describes the electromagnetic fluctuations in a plasma. Our description
includes thermal and collisional effects in a plasma. The electromagnetic
spectrum obtained differs from the blackbody spectrum in vacuum at low
frequencies. In particular, concentrating on the primordial nucleosynthesis
era, it has more energy for frequencies less than 3 to $6\omega_{pe}$, where
$\omega_{pe}$ is the electron plasma frequency.

26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
19
The categories of this paper are: eess
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas