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SUMMARY:Cosmic inhomogeneities with large amplitudes
DTSTART:20261105T130000Z
DTEND:20261105T140000Z
DTSTAMP:20261029T121200Z
UID:indico-event-40968@indico.in2p3.fr
DESCRIPTION:Speakers: Julien Grain (Institut d'Astrophysique Spatiale (IAS
 ) /Université Paris Saclay)\n\nIn the standard model of cosmology\, all l
 arge-scale structures emerge from tiny density fluctuations produced durin
 g inflation. In this setup\, cosmic inhomogeneities of primordial origin a
 re extracted out of the quantum fluctuations of the matter and gravitation
 al fields. Their production is usually treated by means of perturbation th
 eory and quantum fields theory on curved spaces. Yet\, primordial fluctuat
 ions with large amplitudes are also expected to form. They are rare but st
 rongly impacted by non-linearities\, and they drastically modify the emerg
 ence of structures as dark matter halos and cosmic voids. Stochastic infla
 tion is the main approach to deal with the large-amplitude regime. It is a
 n open effective theory expected to capture non-linear evolution at large 
 scale in a non-perturbative manner. It relies on the separate-universe app
 roximation and the quantum-to-classical transition of cosmological perturb
 ations that I will discuss. As a result\, the statistics of cosmic inhomog
 eneities is obtained averaging over independent patches of the universe\, 
 as each evolves as a random walk. Using large-deviation theory\, I will sh
 ow strong departure from gaussianity for over- and underdensities with lar
 ge amplitudes\, and highlight their impact on the abundances of cosmic str
 uctures. It also means that our Hubble patch results from a random process
 . It leads to extra-variability of cosmological parameters that I will ill
 ustrate considering large-scale anisotropy. If time permits\, I will discu
 ss in more details the quantum-to-classical transition in the light of dec
 oherence and open quantum systems.\n\nhttps://indico.in2p3.fr/event/40968/
LOCATION:Amphi G.Besse (Subatech IMT Atlantique)
URL:https://indico.in2p3.fr/event/40968/
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