Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Precision Neutrino Counting   In the framework of the standard, hot big bang cosmological model the
dynamics of the early evolution of the universe is controlled by the energy
density of relativistic particles, among which neutrinos play an important
role. In equilibrium, the energy density contributed by one flavor of
relativistic neutrinos is 7/8 of that of the cosmic background radiation (CBR)
photons. As the universe expands and cools, neutrinos decouple and their
subsequent contribution to the energy density is modified by the relative
heating of the CBR photons when electron-positron pairs annihilate. The small
corrections to the post-annihilation energy density of the standard model
neutrinos due to incomplete decoupling and finite-temperature QED effects are
reviewed (correcting an error in the literature) and extended to account for
possible additional relativistic degrees of freedom whose presence might modify
the predictions of primordial nucleosynthesis and of the predicted CBR
anisotropies.

5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics