paper

Non-parametric exploration of minimally coupled gravity with phantom crossing

arXiv:2512.13691 · doi:10.1103/ckns-5ytv

Abstract

Recent measurements of the baryon acoustic oscillations by the Dark Energy Spectroscopic Instrument (DESI), especially when combined with cosmic microwave background (CMB) and supernova data, favor a late-time dark energy equation of state that crosses , which has been argued to point toward non-minimal conformal coupling in Horndeski gravity. We test this interpretation by performing a non-parametric exploration of the minimally coupled, luminal Horndeski subclass known as kinetic gravity braiding (KGB). Using mochi_class and its manifestly stable effective field theory (EFT) basis implementation, we efficiently scan a broad class of models in which the EFT functions are allowed to vary freely in time, while enforcing the absence of ghost and gradient instabilities from the outset. We identify a set of KGB models that realize phantom crossing and remain broadly consistent with current probes of the background and linear large-scale structure, including CMB temperature and lensing power spectra, redshift-space distortions, cosmic shear, and the cross-correlation between galaxies and the Integrated Sachs-Wolfe effect. Our results demonstrate that viable phantom-crossing solutions exist without conformal coupling, motivating future full Bayesian analyses of this model class with non-parametric EFT priors.

11 pages, 6 figures; very minor changes to match accepted version

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