Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Initial time singularities and admissible initial states for a system of
  coupled scalar fields   We discuss the problem of initial states for a system of coupled scalar
fields out of equilibrium in the one-loop approximation. The fields consist of
classical background fields, taken constant in space, and quantum fluctuations.
If the initial state is the adiabatic vacuum, i.e., the ground state of a Fock
space of particle excitations that diagonalize the mass matrix, the
energy-momentum tensor is infinite at t=0, its most singular part behaves as
1/t. When the system is coupled to gravity this presents a problem that we
solve by a Bogoliubov transformation of the naive initial state. As a side
result we also discuss the canonical formalism and the adiabatic particle
number for such a system. Most of the formalism is presented for Minkowksi
space. Embedding the system and its dynamics into a flat FRW universe is
straightforward and we briefly address the essential modifications.

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The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol