How strong is the evidence for accelerated expansion?

We test the present expansion of the universe using supernova type Ia data without making any assumptions about the matter and energy content of the universe or about the parameterization of the deceleration parameter. We assume the cosmological principle to apply in a strict sense. The result strongly depends on the data set, the light-curve fitting method and the calibration of the absolute magnitude used for the test, indicating strong systematic errors. Nevertheless, in a spatially flat universe there is at least a 5 sigma evidence for acceleration which drops to 1.8 sigma in an open universe.Comment: 16 pages, 3 figure

Cosmodynamics: Energy conditions, Hubble bounds, density bounds, time and distance bounds

We refine and extend a programme initiated by one of the current authors [Science 276 (1997) 88; Phys. Rev. D56 (1997) 7578] advocating the use of the classical energy conditions of general relativity in a cosmological setting to place very general bounds on various cosmological parameters. We show how the energy conditions can be used to bound the Hubble parameter H(z), Omega parameter Omega(z), density rho(z), distance d(z), and lookback time T(z) as (relatively) simple functions of the redshift z, present-epoch Hubble parameter H_0, and present-epoch Omega parameter Omega_0. We compare these results with related observations in the literature, and confront the bounds with the recent supernova data.Comment: 21 pages, 2 figure

Light propagation in statistically homogeneous and isotropic universes with general matter content

We derive the relationship of the redshift and the angular diameter distance to the average expansion rate for universes which are statistically homogeneous and isotropic and where the distribution evolves slowly, but which have otherwise arbitrary geometry and matter content. The relevant average expansion rate is selected by the observable redshift and the assumed symmetry properties of the spacetime. We show why light deflection and shear remain small. We write down the evolution equations for the average expansion rate and discuss the validity of the dust approximation.Comment: 42 pages, no figures. v2: Corrected one detail about the angular diameter distance and two typos. No change in result

Constraints on anisotropic cosmic expansion from supernovae

Kalus B, Schwarz D, Seikel M, Wiegand A. Constraints on anisotropic cosmic expansion from supernovae. Astronomy &amp; Astrophysics. 2013;553: A56.We test the isotropy of the expansion of the Universe by estimating thehemispherical anisotropy of supernova type Ia (SN Ia) Hubble diagrams at lowredshifts (z<0.2). We compare the best fit Hubble diagrams in pairs of hemispheres and searchfor the maximal asymmetric orientation. For an isotropic Universe, we expectonly a small asymmetry due to noise and the presence of nearby structures. Thistest does not depend on the assumed content of the Universe, the assumed modelof gravity, or the spatial curvature of the Universe. The expectation forpossible fluctuations due to large scale structure is evaluated for the \Lambdacold dark matter (\Lambda CDM) model and is compared to the supernova data fromthe Constitution set for four different light curve fitters, thus allowing astudy of the systematic effects. The expected order of magnitude of the hemispherical asymmetry of the Hubbleexpansion agrees with the observed one. The direction of the Hubble asymmetryis established at 95% confidence level (C.L.) using both, the MLCS2k2 and theSALT II light curve fitter. The highest expansion rate is found towards (l, b)~ (-35{\deg},-19{\deg}), which agrees with directions reported by otherstudies. Its amplitude is not in contradiction to expectations from the \LambdaCDM model. The measured Hubble anisotropy is \Delta H/H ~ 0.026. With 95% C.L.the expansion asymmetry is \Delta H/H<0.038