Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmic fluctuations from quantum effective action   Does the observable spectrum of cosmic fluctuations depend on detailed
initial conditions? This addresses the question if the general inflationary
paradigm is sufficient to predict within a given model the spectrum and
amplitude of cosmic fluctuations, or if additional particular assumptions about
the initial conditions are needed. The answer depends on the number of
e-foldings $N_{in}$ between the beginning of inflation and horizon crossing of
the observable fluctuations. We discuss an interacting inflaton field in an
arbitrary homogeneous and isotropic geometry, employing the quantum effective
action $\Gamma$. An exact time evolution equation for the correlation function
involves the second functional derivative $\Gamma^{(2)}$. The operator
formalism and quantum vacua for interacting fields are not needed. Use of the
effective action also allows one to address the change of frames by field
transformations (field relativity). Within the approximation of a derivative
expansion for the effective action we find the most general solution for the
correlation function, including mixed quantum states. For not too large
$N_{in}$ the memory of the initial conditions is preserved. In this case the
cosmic microwave background cannot disentangle between the initial spectrum and
its processing at horizon crossing. The inflaton potential cannot be
reconstructed without assumptions about the initial state of the universe. We
argue that for very large $N_{in}$ a universal scaling form of the correlation
function is reached for the range of observable modes. This can be due to
symmetrization and equilibration effects, not yet contained in our
approximation, which drive the short distance tail of the correlation function
towards the Lorentz invariant propagator in flat space.

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The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
23
The categories of this paper are: solv-int
36
The categories of this paper are: cmp-lg
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The categories of this paper are: cs
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ