Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Hamiltonian formalism for scalar fields coupled to gravity in a
  cosmological background   A novel routine to investigate the scalar fields in a cosmological context is
discussed in the framework of the Hamiltonian formalism. Starting from the
Einstein-Hilbert action coupled to a Lagrangian density that contains two
components - one corresponding to a scalar field Lagrangian,
${\mathcal{L}}_{\phi}$, and another that depends on the scale parameter,
${\mathcal{L}}_{a}$ - one can identify a generalized Hamiltonian density from
which first-order dynamical equations can be obtained. This set up corresponds
to the dynamics of Friedmann-Robertson-Walker models in the presence of
homogeneous fields embedded into a generalized cosmological background fluid in
a system that evolves all together isentropically. Once the generalized
Hamiltonian density is properly defined, the constraints on the
gravity-matter-field system are straightforwardly obtained through the
first-order Hamilton equations. The procedure is illustrated for three examples
of cosmological interest for studies of the dark sector: real scalar fields,
tachyonic fields and generalized Born-Infeld tachyonic fields. The inclusion of
some isentropic fluid component into the Friedmann equation allows for
identifying an exact correspondence between the dark sector underlying scalar
field and an ordinary real scalar field dynamics. As a final issue, the
Hamiltonian formulation is used to set the first-order dynamical equations
through which one obtains the exact analytical description of the cosmological
evolution of a generalized Chaplygin gas (GCG) with dustlike matter, radiation
or curvature contributions. Model stability in terms of the square of the sound
velocity, $c_{s}^{2}$, cosmic acceleration, $q$, and conditions for inflation
are discussed.

22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga