Metastable Dark Energy on the Phantom Brane

Abstract

Recent DESI observations hint at a preference for dynamical dark energy with an equation of state (EoS) that crosses the phantom divide at $w=-1$. In this work, we investigate \textit{metastable} dark energy (DE) on the minimal phantom brane. Braneworld effects lead to $w<-1$ at early times, whereas metastable decay of DE results in $w>-1$ at late times. We consider three metastable decay prescriptions on the phantom brane: an exponentially decaying DE component (M1), decay of DE into non-baryonic dark matter (M2), and decay into dark radiation (M3). Using CMB observations, DESI DR2 BAO measurements, and the DES-Dovekie Type Ia supernova sample, we compare these models with $\Lambda$CDM, the Chevallier--Polarski--Linder (CPL) parametrization, and the minimal phantom-brane model with a non-decaying $\Lambda$. We find that metastable models on the brane are preferred over $\Lambda$CDM, their decay rates being $\Gamma /H_0=0.362\pm 0.086$, $0.539\pm 0.125$, and $0.483\pm 0.112$ for M1, M2, and M3, respectively. Best fits of metastable models improve over $\Lambda$CDM by $\Delta {\chi }_{\mathrm{MAP}}^2=-17.14$, $-18.76$, and $-18.22$, while the corresponding $\Delta \mathrm{DIC}$ values are $-8.66$, $-9.63$, and $-6.56$. Braneworld screening drives effective phantom behaviour at $z\gtrsim 0.4$, while DE decay drives the EoS toward non-phantom values closer to the present epoch, with the phantom divide $w=-1$ being crossed at $z\simeq 0.3$--$0.4$. These results show that the interplay between metastable decay and phantom-brane screening provides a simple physical mechanism for an effective crossing of the phantom divide consistent with DESI observations.

11 pages, 7 figures. Comments are welcome