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SUMMARY:Steps toward  relativistic structure formation: a  nonlinear post-
 Friedmann framework  for small and large  scales - Marco Bruni (ICG Portsm
 outh)
DTSTART:20141110T130000Z
DTEND:20141110T140000Z
UID:TALK55369@talks.cam.ac.uk
CONTACT:33215
DESCRIPTION:Deviations from homogeneity in cosmology are traditionally stu
 died with different methods at small and large scales. In studies of the e
 arly Universe and at scales of the order of the Hubble horizon today\, sma
 ll fluctuations are investigated with relativistic perturbation theory. No
 n-linear structure formation at small scales is instead studied with Newto
 nian methods\, notably N-body simulations. \n In view of new large-scale g
 alaxy surveys that will provide data with an unprecedented accuracy\, it s
 eems timely to go beyond the Newtonian approximation\, unifying the study 
 of the very large scales and the small non-linear scales in a single theor
 etical framework. In this talk I will describe a sort of post-Minkowskian 
 (weak field) approach to cosmology\, such that at leading order in a 1/c e
 xpansion Newtonian cosmology is recovered as a consiste approximate soluti
 on of Einstein equations\, on top of a Friedmannian background. In this po
 st-Friedmann framework\, linear and  non-linear relativistic contributions
  appear  at next order. Resumming variables and linearising the equations 
 one recovers first-order relativistic perturbation theory\, i.e. the frame
 work is valid on horizon scales and beyond. I will \nillustrate the first 
 practical application\, i.e. the extraction of the frame-dragging gravitom
 agnetic potential from N-body simulations\, and its power spectrum.  Simil
 arly\, the difference between the two scalar potential\, known as "slip" i
 n cosmology\, can also in principle be computed\, sourced at leading order
  by purely Newtonian non-linear terms. I will conclude with an outlook on 
 possible further developments.
LOCATION:CMS\, Pav. B\, CTC Common Room (B1.19) [Potter Room]
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