Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Rigorous Formulation of Duality in Gravitational Theories   In this paper we evince a rigorous formulation of duality in gravitational
theories where an Einstein like equation is valid, by providing the conditions
under which the Hodge duals (with respect to the metric tensor g) of T^a and
R_b^a may be considered as the torsion and curvature 2-forms associated with a
connection D', part of a Riemann-Cartan structure (M,g',D'), in the cases g =
g' and g does not equal g', once T^a and R_b^a are the torsion and curvature
2-forms associated with a connection D part of a Riemann-Cartan structure
(M,g,D). A new form for the Einstein equation involving the dual of the Riemann
tensor of D is also provided, and the result is compared with others appearing
in the literature.

6
The categories of this paper are: astro-ph
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
28
The categories of this paper are: alg-geom
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con