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SUMMARY:Plenary — Antonio De Felice: From Data to Dynamics: A Simple Pha
 ntom-Crossing Dark Energy Parametrization
DTSTART;VALUE=DATE-TIME:20261116T040000Z
DTEND;VALUE=DATE-TIME:20261116T050000Z
DTSTAMP;VALUE=DATE-TIME:20261026T160504Z
UID:indico-contribution-1063@indico.narit.or.th
DESCRIPTION:Is the time dependence of dark energy genuinely complicated\, 
 or can current observations be described by a much simpler expression?\n\n
 I will present a data-driven approach to this question within VCDM\, a min
 imally modified theory of gravity that allows a consistent treatment of co
 smological perturbations even when the effective dark-energy equation of s
 tate crosses the phantom divide.\n\nWe begin by reconstructing the dark-en
 ergy equation of state using Bayesian splines constrained by cosmic microw
 ave background\, baryon acoustic oscillation\, and Type Ia supernova obser
 vations. The reconstruction favors relatively smooth histories\, while Bay
 esian evidence does not justify introducing excessive functional complexit
 y. We then employ exhaustive symbolic regression to identify compact and i
 nterpretable analytic expressions compatible with the reconstructed evolut
 ion.\n\nA particularly interesting outcome is the one-parameter form \\(w(
 a) = w_0/\\sqrt{a}\\)\, which provides a competitive fit compared with con
 ventional two-parameter parametrizations\, including CPL.\n\nIts simplicit
 y leads to concrete predictions: the phantom-crossing redshift is determin
 ed by the single parameter \\(w_0\\)\, the effective dark-energy density i
 s suppressed at early times\, and the phantom phase is transient\, avoidin
 g a future big-rip singularity.\n\nI will discuss the observational implic
 ations of this result and explain how the underlying VCDM dynamics can acc
 ommodate phantom crossing without introducing an additional propagating sc
 alar degree of freedom.\n\nhttps://indico.narit.or.th/event/234/contributi
 ons/1063/
LOCATION:Pattaya\, Thailand D Varee Jomtien Beach Pattaya Hotel
URL:https://indico.narit.or.th/event/234/contributions/1063/
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