Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Revisiting constraints on small scale perturbations from big-bang
  nucleosynthesis   We revisit the constraints on the small scale density perturbations
($10^4\,\mathrm{Mpc}^{-1}\lesssim k \lesssim10^5\,\mathrm{Mpc}^{-1}$) from the
modification of the freeze-out value of the neutron-proton ratio at big-bang
nucleosynthesis era. Around the freeze-out temperature $T\sim
0.5\,\mathrm{MeV}$, the universe can be divided into several local patches
which have different temperatures since any perturbation which enters the
horizon after the neutrino decoupling has not diffused yet. Taking account of
this situation, we calculate the freeze-out value in detail. We find that the
small scale perturbations decrease the n-p ratio in contrast to previous works.
With use of the latest observed $^4$He abundance, we obtain the constraint on
the power spectrum of the curvature perturbations as
$\Delta^2_\mathcal{R}\lesssim 0.018$ on $10^4\,\mathrm{Mpc}^{-1}\lesssim k
\lesssim 10^5\,\mathrm{Mpc}^{-1}$.

18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
7
The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
2
The categories of this paper are: math
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics