Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Analytical Approximation to the Nonlinear Power Spectrum of
  Gravitational Clustering   This paper presents an analytical formula that closely approximates the fully
nonlinear power spectrum of matter fluctuations for redshift $z\approx 5$ to 0
over a wide range of cosmologically interesting flat models with varying matter
density $\Omega_m$ and neutrino fraction $\Omega_\nu$. The functional form is
motivated by analytical solutions in asymptotic regimes, but in order to obtain
accurate approximations, the coefficients are calculated from fits to the
nonlinear power spectrum computed from numerical simulations of four
cosmological models. The transformation from the linear to nonlinear power
spectrum depends on $\Omega_m, \Omega_\nu$, and time. A simple scaling rule is
introduced, which greatly simplifies the construction of the functional form
and allows the formula to depend directly on the rms linear mass fluctuation
$\sigma_8$ instead of on an effective spectral index as in earlier work.

7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int