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SUMMARY:Plenary — Atsushi Naruko: Understanding Cosmological Perturbatio
 ns through the Separate-Universe Approach
DTSTART;VALUE=DATE-TIME:20261119T060000Z
DTEND;VALUE=DATE-TIME:20261119T070000Z
DTSTAMP;VALUE=DATE-TIME:20261026T170147Z
UID:indico-contribution-1074@indico.narit.or.th
DESCRIPTION:How much can we learn about an inhomogeneous universe from hom
 ogeneous background solutions? The separate-universe approach offers a rem
 arkably simple way to address this question: on sufficiently large scales\
 , different regions of the universe can be treated approximately as homoge
 neous universes\, allowing us to follow the nonlinear evolution of cosmolo
 gical perturbations without solving the full inhomogeneous equations.\n\nI
 n this talk\, I will introduce the basic physical picture of the separate-
 universe approach and its formulation in terms of the spatial gradient exp
 ansion. I will then explain how this leads to the δN formalism\, which re
 lates large-scale curvature perturbations to differences in the local expa
 nsion history. I will also discuss the assumptions underlying this descrip
 tion\, why it works\, and where its limitations become important. Finally\
 , I will briefly touch upon extensions of the standard framework and recen
 t developments in the study of nonlinear cosmological perturbations. The a
 im is to provide an accessible overview of the subject\, emphasizing physi
 cal intuition and its usefulness for understanding the early universe.\n\n
 https://indico.narit.or.th/event/234/contributions/1074/
LOCATION:Pattaya\, Thailand D Varee Jomtien Beach Pattaya Hotel
URL:https://indico.narit.or.th/event/234/contributions/1074/
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