Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: WKB approximation for inflationary cosmological perturbations   A new method for predicting inflationary cosmological perturbations, based on
the Wentzel-Kramers-Brillouin (WKB) approximation, is presented. A general
expression for the WKB scalar and tensor power spectra is derived. The main
advantage of the new scheme of approximation is that it is valid even if the
slow-roll conditions are violated. The method is applied to power-law
inflation, which allows a comparison with an exact result. It is demonstrated
that the WKB approximation predicts the spectral indices exactly and the
amplitude with an error lower than 10%, even in regimes far from
scale-invariance. The new method of approximation is also applied to a
situation where the slow-roll conditions hold. It is shown that the result
obtained bears close resemblance with the standard slow-roll calculation.
Finally, some possible improvements are briefly mentioned.

10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an