263 research outputs found
Variation of the constants in the late and early universe
Recent key observational results on the variation of fine structure constant,
the proton to electron mass ratio and the gravitational constant are reviewed.
The necessity to substantiate the dark sector of cosmology and to test gravity
on astrophysical scales is also emphasized.Comment: 19 pages, 6 figures, Invited talk at the conference "The Quest for
Cosmological Scalar Fields", Porto, 8-10 July 200
Quantization of perturbations during inflation in the 1+3 covariant formalism
This note derives the analogue of the Mukhanov-Sasaki variables both for
scalar and tensor perturbations in the 1+3 covariant formalism. The possibility
of generalizing them to non-flat Friedmann-Lemaitre universes is discussed.Comment: 4 pages: v2 has minor changes to match published versio
From configuration to dynamics -- Emergence of Lorentz signature in classical field theory
The Lorentzian metric structure used in any field theory allows one to
implement the relativistic notion of causality and to define a notion of time
dimension. This article investigates the possibility that at the microscopic
level the metric is Riemannian, i.e. locally Euclidean, and that the Lorentzian
structure, that we usually consider as fundamental, is in fact an effective
property that emerges in some regions of a 4-dimensional space with a positive
definite metric. In such a model, there is no dynamics nor signature flip
across some hypersurface; instead, all the fields develop a Lorentzian dynamics
in these regions because they propagate in an effective metric. It is shown
that one can construct a decent classical field theory for scalars, vectors and
(Dirac) spinors in flat spacetime. It is then shown that gravity can be
included but that the theory for the effective Lorentzian metric is not general
relativity but of the covariant Galileon type. The constraints arising from
stability, the equivalence principle and the constancy of fundamental constants
are detailed and a phenomenological picture of the emergence of the Lorentzian
metric is also given. The construction, while restricted to classical fields in
this article, offers a new view on the notion of time.Comment: 19 pages, 2 figures; published versio
Cosmic Strings Lens Phenomenology Revisited
We present investigations of lens phenomenological properties of cosmic
strings for deep galaxy surveys. General results that have obtained for lineic
energy distribution are presented first. We stress that generically the local
convergence always vanishes in presence of strings although there might be some
significant distortions. We then propose a simplified model of strings, we call
``Poisson strings'', for which exhaustive investigations can be done either
numerically or analytically.Comment: 6 pages; To appear in the Proceedings of the XXth Moriond
Astrophysics Meeting "Cosmological Physics with Gravitational Lensing", eds.
J.-P. Kneib, Y. Mellier, M. Moniez and J. Tran Thanh Van, Les Arcs, France,
March 11th-18th 200
Late time anisotropy as an imprint of cosmological backreaction
Backreaction effects of the large scale structure on the background dynamics
have been claimed to lead to a renormalization of the background dynamics that
may account for the late time acceleration of the cosmic expansion. This
article emphasizes that generically the averaged flow is locally anisotropic, a
property that can be related to observation. Focusing on perturbation theory,
the spatially averaged shear, that characterizes the anisotropy of the flow, is
computed. It is shown that this shear arising from backreaction differs from a
homogeneous shear: its time evolution is different and its amplitude is
completely determined by the cosmological parameters and the matter power
spectrum. It ranges within (2-37)% at a redshift of order 0.5 so that the
isotropy of the Hubble flow may allow to constrain the backreaction approach to
dark energy.Comment: 14 pages, 7 figures. Typos corrected. Article published in Phys. Rev.
D 86, 063528 (2012
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