Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The necessity of non-Riemannian acoustic spacetime in the fluids with
  vorticity   The necessity of a newly proposed (PRD 70 (2004) 64004) non-Riemannian
acoustic spacetime structure called acoustic torsion of sound wave equation in
fluids with vorticity are discussed. It is shown that this structure, although
not always necessary is present in fluids with vorticity even when the
perturbation is rotational. This can be done by solving the Bergliaffa et al
(Physica D (2004)) gauge invariant equations for sound, superposed to a general
background flow, needs to support a non-Riemannian acoustic geometry in
effective spacetime. Bergliaffa et al have previously shown that a Riemannian
structure cannot be associated to this gauge invariant general system.

27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
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
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
1
The categories of this paper are: cs
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
3
The categories of this paper are: physics
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol