Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Note on scalars, perfect fluids, constrained field theories, and all
  that   The relation of a scalar field with a perfect fluid has generated some debate
along the last few years. In this paper we argue that shift-invariant scalar
fields can describe accurately the potential flow of an isentropic perfect
fluid, but, in general, the identification is possible only for a finite period
of time. After that period in the evolution the dynamics of the scalar field
and the perfect fluid branch off. The Lagrangian density for the
velocity-potential can be read directly from the expression relating the
pressure with the Taub charge and the entropy per particle in the fluid,
whereas the other quantities of interest can be obtained from the thermodynamic
relations.

37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org