717 research outputs found
A Strong Constraint on Ever-Present Lambda
We show that the causal set approach to creating an ever-present cosmological
'constant' in the expanding universe is strongly constrained by the isotropy of
the microwave background. Fluctuations generated by stochastic lambda
generation which are consistent with COBE and WMAP observations are far too
small to dominate the expansion dynamics at z<1000 and so cannot explain the
observed late-time acceleration of the universe. We also discuss other
observational constraints from the power spectrum of galaxy clustering and show
that the theoretical possibility of ever-present lambda arises only in 3+1
dimensional space-times.Comment: 5 pages, minor additions, published versio
Simple Types of Anisotropic Inflation
We display some simple cosmological solutions of gravity theories with
quadratic Ricci curvature terms added to the Einstein-Hilbert lagrangian which
exhibit anisotropic inflation. The Hubble expansion rates are constant and
unequal in three orthogonal directions. We describe the evolution of the
simplest of these homogeneous and anisotropic cosmological models from its
natural initial state and evaluate the deviations they will create from
statistical isotropy in the fluctuations produced during a period of
anisotropic inflation. The anisotropic inflation is not a late-time attractor
in these models but the rate of approach to a final isotropic de Sitter state
is slow and is conducive to the creation of observable anisotropic statistical
effects in the microwave background. The statistical anisotropy would not be
scale invariant and the level of statistical anisotropy will grow with scale.Comment: 8pages, 3 figs v2:refs added, typos fixe
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