4 research outputs found
Symmetry analysis and exact solutions of modified Brans-Dicke cosmological equations
We perform a symmetry analysis of modified Brans-Dicke cosmological equations
and present exact solutions. We discuss how the solutions may help to build
models of cosmology where, for the early universe, the expansion is linear and
the equation of state just changes the expansion velocity but not the
linearity. For the late universe the expansion is exponential and the effect of
the equation of state on the rate of expansion is just to change the constant
Hubble parameter.Comment: LaTeX2e source file, 14 pages, 7 reference
Can hyperbolic phase of Brans-Dicke field account for Dark Matter?
We show that the introduction of a hyperbolic phase for Brans-Dicke (BD)
field results in a flat vacuum cosmological solution of Hubble parameter H and
fractional rate of change of BD scalar field, F which asymptotically approach
constant values. At late stages, hyperbolic phase of BD field behaves like dark
matter
Chiral spinors and gauge fields in noncommutative curved space-time
The fundamental concepts of Riemannian geometry, such as differential forms,
vielbein, metric, connection, torsion and curvature, are generalized in the
context of non-commutative geometry. This allows us to construct the
Einstein-Hilbert-Cartan terms, in addition to the bosonic and fermionic ones in
the Lagrangian of an action functional on non-commutative spaces. As an
example, and also as a prelude to the Standard Model that includes
gravitational interactions, we present a model of chiral spinor fields on a
curved two-sheeted space-time with two distinct abelian gauge fields. In this
model, the full spectrum of the generalized metric consists of pairs of tensor,
vector and scalar fields. They are coupled to the chiral fermions and the gauge
fields leading to possible parity violation effects triggered by gravity.Comment: 50 pages LaTeX, minor corrections and references adde
On the ADM decomposition of the 5-D Kaluza-Klein model
Our purpose is to recast KK model in terms of ADM variables. We examine and
solve the problem of the consistency of this approach, with particular care
about the role of the cylindricity hypothesis. We show in details how the KK
reduction commutes with the ADM slicing procedure and how this leads to a well
defined and unique ADM reformulation. This allows us to consider the
hamiltonian formulation of the model and can be the first step for the Ashtekar
reformulation of the KK scheme. Moreover we show how the time component of the
gauge vector arises naturally from the geometrical constraints of the dynamics;
this is a positive check for the autoconsistency of the KK theory and for an
hamiltonian description of the dynamics which wants to take into account the
compactification scenario: this result enforces the physical meaning of KK
model.Comment: 24 pages, no figures, to appear on IJMP