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SUMMARY:Cosmic ruler and cosmic ladder  - Licia Verde (ICREA/ICC Barcelona
  & ITA Oslo)
DTSTART:20150427T120000Z
DTEND:20150427T130000Z
UID:TALK59236@talks.cam.ac.uk
CONTACT:Tommaso Giannantonio
DESCRIPTION:The Baryon Acoustic Oscillation feature is a key observable in
  cosmology\, corresponding to the maximum distance sound waves of baryonic
  matter can travel in the early Universe. It leaves a measurable imprint i
 n the clustering of galaxies at late times\, which can be used as a "stand
 ard ruler”. I will discuss how this feature can be used in combination w
 ith other observations to construct a cosmic distance ladder which strongl
 y constrains the expansion history of the Universe.\nWhile the traditional
  way to build a cosmic distance ladder is to calibrate locally and extend 
 it out to high redshift\, the BAO feature allows us to calibrate at z~1000
  and extend the ladder inwards. In combination with other observations (st
 andard candles and/or standard clocks) it is even possible to measure the 
 expansion history of the Universe\, constrain its spatial curvature\, and 
 determine the length of the standard ruler in a way that is  model indepen
 dent. The better than 1% measurement of the BAO location from galaxy surve
 ys requires a better than 1% modeling for its correct cosmological interpr
 etation. \nWith this approach  one can trade off precision for robustness.
   In fact it is possible to use only very weak assumptions of symmetry and
  a smooth expansion history\,  and one does not even need assuming General
  Relativity. Since the length is set early on in the Universe's history\, 
 the conclusions are independent of late-time physics such as Dark Energy p
 roperties or late modifications to gravity. Even without assuming GR\,  th
 e Universe looks very much like the standard LCDM model.
LOCATION:CMS\, Pav. B\, CTC Common Room (B1.19) [Potter Room]
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