Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Linear Response, Validity of Semi-Classical Gravity, and the Stability
  of Flat Space   A quantitative test for the validity of the semi-classical approximation in
gravity is given. The criterion proposed is that solutions to the
semi-classical Einstein equations should be stable to linearized perturbations,
in the sense that no gauge invariant perturbation should become unbounded in
time. A self-consistent linear response analysis of these perturbations, based
upon an invariant effective action principle, necessarily involves metric
fluctuations about the mean semi-classical geometry, and brings in the
two-point correlation function of the quantum energy-momentum tensor in a
natural way. This linear response equation contains no state dependent
divergences and requires no new renormalization counterterms beyond those
required in the leading order semi-classical approximation. The general linear
response criterion is applied to the specific example of a scalar field with
arbitrary mass and curvature coupling in the vacuum state of Minkowski
spacetime. The spectral representation of the vacuum polarization function is
computed in n dimensional Minkowski spacetime, and used to show that the flat
space solution to the semi-classical Einstein equations for n=4 is stable to
all perturbations on distance scales much larger than the Planck length.

12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs
24
The categories of this paper are: dg-ga