Sunday. Went and saw SOFIA at Köln today! 4 hour wait, but was worth it. Saw the A380 take off, and "wave" (tilt a low altitude flying) at us. Had dinner in Bonn with Dandan and Ralph; encountered a spectacular water-fountain show.
AIfA Master-Kolloquium
Decomposition of the matter power spectrum
Richard Hanson
Environmental effects of the matter and halo power spectra. Halo-biasing depends on halo-mass (well known) as well as scale and environment. Separate knots, filaments, sheets and voids: four characteristic environments. Further aspects of the method highlighted.
1109.2314
Does the growth of structure affect out dynamical models of the universe? The averaging, backreaction and fitting problems in cosmology
Clarkson, Ellis, Larena, Umeh
* backreaction: a modification of the original environment due to the probe particle carrying a mass and charge itself. In theoretical physics, back-reaction is often necessary to calculate the behavior of a particle in an external field. In cosmology the term is used for the measure of the non-commutativity of the averaging procedure and the dynamical evolution of space-time; existence of isotropy scale determined by the length scale at which back-reaction parameter vanishes. Existence of (cosmological) back-reaction scale still needs experimental confirmation.
Important problem for cosmology: determining the influence the small-scale structure in the universe has on its large-scale dynamics and observations. One issue: whether process of smoothing over structure can contribute to an acceleration term and alter the apparent value of the cosmological constant. Are there any other aspects of concordance cosmology that are affected by backreaction effects? This 'averaging problem' is still unanswered, but cannot be ignored in precision cosmology.
* basically just states the issue, no resolutions here.
1109.2484
Interpreting supernovae observations in a lumpy universe
Clarkson, Ellis, Faltenbacher, Maartens, Umeh, Uzan
How does may beam (i.e., the light from SNe) averages of Weyl curvature into the Ricci curvature of the background? This is not understood. Incorrect modeling leads to significant changes to the inferred background cosmology. Standard analysis predict a huge variance for small beam sizes; non-linear corrections appear to be non-trivial. Different reasonable apporximations yield very different cosmologies; modelling ultra-narrow beams accurately is a critical problem for precision cosmology.
* this is true for WL cosmic shear too, most likely.
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