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SUMMARY:Cosmological Imprints of the Ultra-Large Scale Universe - Jonathan
  Braden (UCL)
DTSTART:20170213T130000Z
DTEND:20170213T140000Z
UID:TALK70172@talks.cam.ac.uk
CONTACT:47984
DESCRIPTION:Inflation provides a dynamical mechanism to seed density fluct
 uations that eventually collapse to form all of the structure in the obser
 vable universe.  However\, microphysical theories of inflation often predi
 ct that on scales much larger than our present horizon\, the universe may 
 be extremely inhomogeneous.  In general\, this inhomogeneity may manifest 
 in both adiabatic and isocurvature modes.\n\nOne possible source of such u
 ltra-large scale inhomogeneity is from the initial conditions preceding th
 e inflationary phase.  Using numerical relativity\, I will discuss the ult
 ra-large scale structure arising from initial fluctuations in the inflaton
 \, in particular the contribution to the CMB quadrupole (known as the Gris
 chuk-Zel'dovich effect).  For large fluctuations\, the resulting distribut
 ion is strongly distorted from the Gaussian form usually assumed in the li
 terature.  Surprisingly\, we find that this leads to weaker constraints on
  large amplitude initial fluctuations than small amplitude ones.\n\nI will
  also briefly discuss an additional source of inhomogeneity: the nonlinear
  conversion of isocurvature perturbations into adiabatic modes during the 
 post-inflation phase of preheating.  This produces a generalised form of l
 ocal nonGaussian density perturbations\, which exhibits a high degree of s
 patial intermittency.  Remarkably\, I will show how the main features can 
 be understood from the dynamics of decoupled field trajectories undergoing
  chaotic ballistic motion in a potential.
LOCATION:CMS\, Pav. B\, CTC Common Room (B1.19) [Potter Room]
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