Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Classical and Quantum Solutions and the Problem of Time in $R^2$
  Cosmology   We have studied various classical solutions in $R^2$ cosmology. Especially we
have obtained general classical solutions in pure $R^2$\ cosmology. Even in the
quantum theory, we can solve the Wheeler-DeWitt equation in pure $R^2$\
cosmology exactly. Comparing these classical and quantum solutions in $R^2$\
cosmology, we have studied the problem of time in general relativity.

26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th