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SUMMARY:The screening Horndeski cosmologies
DTSTART;VALUE=DATE-TIME:20161011T104500Z
DTEND;VALUE=DATE-TIME:20161011T110000Z
DTSTAMP;VALUE=DATE-TIME:20260713T094922Z
UID:indico-contribution-506@cern.ch
DESCRIPTION:Speakers: Sergey Sushkov (Kazan Federal University)\nWe presen
 t a systematic  analysis of  homogeneous and isotropic cosmologies in a  p
 articular Horndeski model with Galileon shift symmetry\, containing also a
  $\\Lambda$-term and a matter. The model\, sometimes called Fab Five\, adm
 its a rich spectrum of  solutions. Some of them describe the standard late
  time cosmological dynamic dominated by the $\\Lambda$-term and matter\, w
 hile at the early times the universe expands with a constant Hubble rate d
 etermined by the value of the scalar  kinetic coupling. For other solution
 s the $\\Lambda$-term and  matter are screened at all times  but there are
   nevertheless  the early and late accelerating phases. The model also adm
 its bounces\, as well as peculiar solutions describing ``the emergence of 
 time''. Most of these solutions contain ghosts in the scalar and tensor se
 ctors. However\, a careful analysis reveals three different branches of gh
 ost-free solutions\, all showing a late time acceleration phase. We analys
 e the dynamical stability of these\nsolutions and find that all of them ar
 e stable in the future\, since all their perturbations stay bounded at lat
 e times. However\, they all turn out to be unstable in the past\, as their
  perturbations grow  violently   when one approaches the initial spacetime
  singularity. We therefore conclude that the model has no viable solutions
  describing the whole of the cosmological history\, although it may descri
 be the current\nacceleration phase. We also check that the flat space solu
 tion is ghost-free in the model\, but it may acquire ghost in more general
  versions of the Horndeski theory.\n\nhttps://indico.particle.mephi.ru/eve
 nt/4/contributions/506/
LOCATION:Milan Hotel Rossini
URL:https://indico.particle.mephi.ru/event/4/contributions/506/
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