Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: From vacuum field equations on principal bundles to Einstein equations
  with fluids   In the present work we show that the Einstein equations on $M$ without
cosmological constant and with perfect fluid as source, can be obtained from
the field equations for vacuum with cosmological constant on the principal
fibre bundle $P(\frac{1}{I} M,U(1))$, $M$ being the space-time and $I$ the
radius of the internal space $U(1)$.

29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat
3
The categories of this paper are: physics