Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the initial value problem for the wave equation in Friedmann --
  Robertson -- Walker space-times   We study the wave propagator for a Friedmann - Robertson - Walker background
space-time, which is singular at time t=0. Using a spherical means formulation
for the solution of the wave equation that is due to Klainerman and Sarnak, we
derive three properties of solutions. the first is sharp time decay properties,
using ideas of Fritz John. the second is that the wave equation in Friedmann -
Robertson - Walker space-time does not satisfy the sharp Huygens property. The
third is that the initial value problem for a class of data posed at the
tingular time is well defined. Since the wave equation is reversible, this
represents a class of data which propagates information smoothly from the past
to the future passing through the space-time singularity.

24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
1
The categories of this paper are: cs
16
The categories of this paper are: stat
17
The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas