Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Blue and violet graviton spectra from a dynamical refractive index   We show that the spectral energy distribution of relic gravitons mildly
increases for frequencies smaller than the $\mu$Hz and then flattens out
whenever the refractive index of the tensor modes is dynamical during a
quasi-de Sitter stage of expansion. For a conventional thermal history the
high-frequency plateau ranges between the mHz and the audio band but it is
supplemented by a spike in the GHz region if a stiff post-inflationary phase
precedes the standard radiation-dominated epoch. Even though the slope is blue
at intermediate frequencies, it may become violet in the MHz window. For a
variety of post-inflationary histories, including the conventional one, a
dynamical index of refraction leads to a potentially detectable spectral energy
density in the kHz and in the mHz regions while all the relevant
phenomenological constraints are concurrently satisfied.

9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol