Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: In-in formalism, pseudo-instantons and rethinking quantum cosmology   Unlike flat space quantum field theories that focus on scattering amplitudes,
the main observables in quantum cosmology are correlation functions. The
systematic way of calculating correlators is called in-in formalism, which
requires only a single asymptotic region, i.e. past infinity. The rules in
perturbation theory and the path integral measure are very different for in-in
and in-out formalisms, and thus the results which are standard in one approach
may not necessarily hold in the other one. We show that stationary phase
approximation works completely different for a scalar in-in path integral.
Hence, in a cosmological background there are solutions, pseudo-instantons,
that allow tunneling between locally stable vacua even in infinite volume,
which is counterintuitive from an in-out perspective. We argue that various
familiar notions of in-out formalism must be reexamined in the in-in formalism,
which might have important consequences for quantum cosmology.

10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
19
The categories of this paper are: eess
28
The categories of this paper are: alg-geom
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas