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The Cosmological Constant
Structure Formation


Basic Idea: If the universe is spatially flat and there is a postive cosmological constant, then there is a smaller matter density in the universe than if there were no cosmological constant. Structure forms by matter falling towards other matter, and with a smaller matter density this happens more slowly because the pull is weaker.

Theory

  • analytical expression
  • faster growth when there is more matter

Systems of interest:

  1. cluster number
    • What clusters are
      most recently collapsed
      rough indicator of number count: Press Schechter
    • What one measures about them
      indicators: number itself, arcs

    Observations

    • Current results not compelling
      controversial selection effects, small sample
    • Future data sets should improve this significantly

  2. bulls eye effect
    • What it is: fingers of god and compression/rarefaction near over/under densities (a problem turned into a feature...)
    • Measure with data: contours of constant density

    Future plans and hopes with this method

    • Useful with upcoming surveys perhaps, under study

  3. weak lensing
    • What it is
      faint blue galaxies, lss
    • What one measures: correlations

    Observations

    • Method: need large area
    • Current Results
      first detections only this past spring
    • Future plans for surveys and vast improvement

Other cosmological tests and questions these systems are used for

Some References


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