Cosmic Microwave Background Limits on Spatially Homogeneous Cosmological Models with a Cosmological Constant
نویسنده
چکیده
We investigate the effect of dark energy on the limits on the shear anisotropy in spatially homogeneous Bianchi cosmological models obtained from measurements of the temperature anisotropies in the cosmic microwave background. We shall primarily assume that the dark energy is modelled by a cosmological constant. In general, we find that there are tighter bounds on the shear than in models with no cosmolog-ical constant, although the limits are (Bianchi) model dependent. In addition, there are special spatially homogeneous cosmological models whose rate of expansion is highly anisotropic, but whose cosmic microwave background temperature is measured to be exactly isotropic at one instant of time.
منابع مشابه
Bulk viscous string cosmological models in Saez – Ballester theory of gravitation
Spatially homogeneous Bianchi type-II, VIII and IX anisotropic, as well as isotropic cosmological models can be obtained in a scalar tensor theory of gravitation proposed by Saez and Ballester (1986) when the source for energy momentum tensor is a bulk viscous fluid containing one-dimensional cosmic strings. All the models obtained and presented here are expanding, non-rotating and accelerating...
متن کاملCosmic microwave background constraints on the epoch of reionization
We use a compilation of cosmic microwave anisotropy data to constrain the epoch of reionization in the Universe, as a function of cosmological parameters. We consider spatially-flat cosmologies, varying the matter density Ω0 (the flatness being restored by a cosmological constant), the Hubble parameter h and the spectral index n of the primordial power spectrum. Our results are quoted both in t...
متن کاملConstraints on Ω Λ and Ω m from Distant Type 1 a Supernovae and Cosmic Microwave
We perform a combined likelihood analysis of the latest cosmic microwave background anisotropy data and distant Type 1a Supernova data of Perlmutter et al. (1998a). Our analysis is restricted to cosmological models where structure forms from adiabatic initial fluctuations characterised by a power-law spectrum with negligible tensor component. Marginalizing over other parameters, our best fit so...
متن کاملAnisotropic universes with isotropic cosmic microwave background radiation
We show the existence of spatially homogeneous but anisotropic cosmological models whose cosmic microwave background temperature is exactly isotropic at one instant of time but whose rate of expansion is highly anisotropic. The existence of these models shows that the observation of a highly isotropic cosmic microwave background temperature cannot alone be used to infer that the universe is clo...
متن کاملLarge Scale Cosmological Anomalies and Inhomogeneous Dark Energy
A wide range of large scale observations hint towards possible modifications on the standard cosmological model which is based on a homogeneous and isotropic universe with a small cosmological constant and matter. These observations, also known as “cosmic anomalies” include unexpected Cosmic Microwave Background perturbations on large angular scales, large dipolar peculiar velocity flows of gal...
متن کامل