Crossing the phantom divide in scalar-tensor and vector-tensor theories

Abstract

DESI observations of baryon acoustic oscillations (BAOs), combined with cosmic microwave background (CMB) and type-Ia supernova (SN Ia) data, suggest that the dark energy equation of state $w_{\mathrm{DE}}$ crosses the phantom divide from $w_{\mathrm{DE}}<-1$ to $w_{\mathrm{DE}}>-1$ at low redshifts. In shift-symmetric Horndeski and generalized Proca theories with luminal gravitational-wave speed and no direct couplings to dark matter, we show that such a phantom-divide crossing is generically difficult without theoretical pathologies. Breaking the shift symmetry in Horndeski theories allows this transition. We construct an explicit model with broken shift symmetry, in which the scalar field has a potential in addition to a Galileon self-interaction and a quadratic kinetic term. This model realizes the desired phantom-divide crossing at low redshifts without introducing ghosts and Laplacian instabilities.

7 pages, 3 figures

Cited by in corpus (5)

• Dark Energy in the DESI Era: A Brief Review of Evidence, Beyond-$\Lambda$CDM Interpretations, and Tensions
• Realizing the phantom-divide crossing with vector and scalar fields
• DESI constraints on two-field quintessence with exponential potentials
• Galileon versus Quintessence: A comparative phase space analysis and late-time cosmic relevance
• Non-parametric exploration of minimally coupled gravity with phantom crossing