School of Physics: HEP Weekly Seminar SeriesSpeaker:Shahin Sheikh-JabbariAffiliation:School of Physi

School of Physics: HEP Weekly Seminar SeriesSpeaker:Shahin Sheikh-JabbariAffiliation:School of Physics, Institute for Research in Fundamental Sciences (IPM) Title of talk:Dipole Cosmology: Towards beyond FLRW frameworkکیهان شناسی دوقطبی : به سوی ورای چهارچوب فریدمان-لومیتر-رابرتسون-واکرDate and time:Tuesday, 25th of April 2023 (5th of Ordibehesht, 1402), 2:00 pm (Tehran zone)Link:https://www.skyroom.online/ch/schoolofphysics/highenergyseminarAbstract:There are various, but still tentative, observations hinting to existence of a cosmic flow or cosmic dipole (preferred direction) in cosmological backgrounds. If substantiated, these observations suggest developing cosmological modeling beyond the usual FLRW setting. I present "dipole cosmological principle" as the most symmetric paradigm  that generalizes the FLRW ansatz and allows for cosmic dipoles. We construct a general dipole cosmology framework and analyze Einstein equations for  the dipole cosmology which beside usual FLRW fields involve cosmic shear (parametrizing the anisotropy in the metric) and the tilt (parametrizing the cosmic flow or cosmic dipole). These equations  are still ordinary differential equations due to homogeneity of the dipole cosmology setting.  We study  dynamics of the expansion rate, anisotropic shear and tilt, in various examples. One our key results  is that the cosmic flow (tilt) can grow in time even while the anisotropy (shear) dies down. Remarkably, this can happen even in an era of late time acceleration. The other key result is that FLRW framework is unstable with respect to perturbations associated with cosmic dipoles. This means having a homogeneous and isotropic cosmology is not a theoretically natural choice.