Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multi-fluid Theory and Cosmology: A Convective Variational Approach to
  Interacting Dark-Sector   This article examines the foundation of the recently developed relativistic
variational formalism[1]. Our work is heavily based on [2, 27] which extends
this approach to the multi-fluid theory and examines its utility in
astrophysics and cosmology. Unlike the extension to the formalism mentioned
above, that looks at the general interaction between different types of matter,
we use the formalism to examine the interaction involving, ordinary matter,
dark matter (DM) and dark energy (DE). We focus on entrainment phenomena
involving the dark-sector constituents.

29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin