Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Differences between scalar field and scalar density solutions   We explore differences between scalar field, and scalar density solutions by
using Robertson-Walker (RW) metric, and also a non-relativistic Hamiltonian is
derived for a scalar density field in the post-Newtonian approximation. The
results are compared with those of scalar field. The expanding universe in RW
metric, and post-Newtonian solution of Klein-Gordon equation are separately
discussed.

22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ