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SUMMARY:Plenary — Shinji Tsujikawa: Dark Energy with Stable Phantom-Divi
 de Crossing: Model Construction and Observational Constraints
DTSTART;VALUE=DATE-TIME:20261116T023000Z
DTEND;VALUE=DATE-TIME:20261116T033000Z
DTSTAMP;VALUE=DATE-TIME:20261026T151407Z
UID:indico-contribution-1062@indico.narit.or.th
DESCRIPTION:Recent cosmological observations have revived interest in dark
  energy whose equation of state evolves from below -1 to above -1 at low r
 edshift. In this talk\, I will discuss how to construct theoretically cons
 istent models realizing this transition and test them against observations
 . I will first explain the obstacles to achieving such a crossing in shift
 -symmetric Horndeski and generalized Proca theories with luminal gravitati
 onal-wave propagation and no direct dark-matter couplings. I will then pre
 sent two ways to overcome these obstacles: introducing a scalar potential 
 that breaks shift symmetry in a Horndeski model\, and combining a generali
 zed Proca vector field with a canonical scalar field. Particular attention
  will be paid to the conditions ensuring the absence of ghost and gradient
  instabilities\, as well as the implications for matter clustering and gra
 vitational lensing. I will also present constraints on a scalar-vector-ten
 sor dark-energy model using the DES five-year supernova sample\, second-re
 lease DESI baryon acoustic oscillation measurements\, compressed cosmic mi
 crowave background constraints\, and growth data from redshift-space disto
 rtions. The results allow stable crossing histories and improve the best-f
 it likelihood relative to flat ΛCDM. I will discuss Bayesian model compar
 ison\, including its sensitivity to theoretical viability conditions and p
 rior normalization\, and the prospects for distinguishing these models thr
 ough cosmic expansion and structure growth.\n\nhttps://indico.narit.or.th/
 event/234/contributions/1062/
LOCATION:Pattaya\, Thailand D Varee Jomtien Beach Pattaya Hotel
URL:https://indico.narit.or.th/event/234/contributions/1062/
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