Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Improved Calculation of the Primordial Gravitational Wave Spectrum in
  the Standard Model   We show that the energy density spectrum of the primordial gravitational
waves has characteristic features due to the successive changes in the
relativistic degrees of freedom during the radiation era. These changes make
the evolution of radiation energy density deviate from the conventional
adiabatic evolution, \rho_r~ a^{-4}, and thus cause the expansion rate of the
universe to change suddenly at each transition which, in turn, modifies the
spectrum of primordial gravitational waves. We take into account all the
particles in the Standard Model of elementary particles. In addition,
free-streaming of neutrinos damps the amplitude of gravitational waves, leaving
characteristic features in the energy density spectrum. Our calculations are
solely based on the standard model of cosmology and particle physics, and
therefore these features must exist. Our calculations significantly improve the
previous ones which ignored these effects and predicted a smooth, featureless
spectrum.

18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
4
The categories of this paper are: cond-mat