35 research outputs found
A tensor theory of space-time as a strained material continuum
The classical theory of strain in material continua is reviewed and
generalized to space-time. Strain is attributed to "external" (matter/energy
fields) and intrinsic sources fixing the global symmetry of the universe
(defects in the continuum). A Lagrangian for space-time is worked out, adding
to the usual Hilbert term an "elastic" contribution from intrinsic strain. This
approach is equivalent to a peculiar tensor field, which is indeed part of the
metric tensor. The theory gives a configuration of space-time accounting both
for the initial inflation and for the late acceleration. Considering also the
contribution from matter the theory is used to fit the luminosity data of type
Ia supernovae, giving satisfactory results.Comment: Revised to match the version accepted for publication in Class.
Quantum Gra
Massive gravitational waves from the Cosmic Defect theory
The Cosmic Defect theory (CD), which is presented elsewhere in this
conference, introduces in the standard Einstein-Hilbert Lagrangian an elastic
term accounting for the strain of space-time viewed as a four-dimensional
physical continuum. In this framework the Ricci scalar acts as the kinetical
term of the strain field whose potential is represented by the additional
terms. Here we are presenting the linearised version of the theory in order to
analyze its implications in the weak field limit. First we discuss the recovery
of the Newtonian limit. We find that the typical static weak field limit
imposes a constraint on the values of the two parameters (Lame coefficients) of
the theory. Once the constraint has been implemented, the typical gravitational
potential turns out to be Yukawa-like. The value for the Yukawa parameter is
consistent with the constraints coming from the experimental data at the Solar
system and galactic scales. We then come to the propagating solutions of the
linearised Einstein equations in vacuo, i.e. to gravitational waves. Here,
analogously with other alternative or extended theories of gravity, the
presence of the strain field produces massive waves, where massive (in this
completely classical context) means subluminal. Furthermore longitudinal
polarization modes are allowed too, thus lending, in principle, a way for
discriminating these waves from the plane GR ones.Comment: Proceedings of 'Invisible Universe International Conference', Paris,
June 29- July 3, 200
Weak-Field Spherically Symmetric Solutions in gravity
We study weak-field solutions having spherical symmetry in gravity; to
this end, we solve the field equations for a non diagonal tetrad, starting from
Lagrangian in the form , where is a small
constant, parameterizing the departure of the theory from GR. We show that the
classical spherically symmetric solutions of GR, i.e. the Schwarzschild and
Schwarzschild-de Sitter solutions, are perturbed by terms in the form and discuss the impact of these perturbations in observational tests.Comment: 11 pages, LaTeX; revised to match the version accepted for
publication in Physical Review
Dark energy as an elastic strain fluid
The origin of the accelerated expansion of the universe is still unclear and new physics is needed on cosmological scales. We propose and test a novel interpretation of dark energy as originated by an elastic strain due to a cosmic defect in an otherwise Euclidean space-time. The strain modifies the expansion history of the universe. This new effective contribution tracks radiation at early times and mimics a cosmological constant at late times. The theory is tested against observations, from nucleosynthesis to the cosmic microwave background and formation and evolution of large scale structure to supernovae. Data are very well reproduced with Lamé parameters of the order of 10^(−52) m^(−2