Speaker:	Zhibang Yao (Leiden University)
Title:	Freezing Gravity: A Model for Dark Energy Crossing the Phantom Divide
Date (JST):	Tue, Jan 27, 2026, 15:30 - 17:00
Place:	Seminar Room A
Abstract:	Recent results from the DESI collaboration showed a tension between measurements of BAO and CMB within the ΛCDM model. A time-varying dark energy (DE) is favored by the data and, when combined with SNIa, provides hints that the equation of state (EoS) of DE crosses the phantom divide. In this talk, I will introduce Freezing Gravity, a recently proposed DE model within the framework of spatially covariant theories. In this model, the cosmological background and perturbations are independently controlled by different sets of coefficients, and the EoS of DE is determined directly by two free functions of time in the Lagrangian. These properties allow us to realize arbitrary background evolutions while simultaneously avoiding ghost and gradient instabilities at the level of linear perturbations. I will further discuss the behavior of the scalar mode in this theory, the potential strong-coupling issue, and the associated energy cut-off scale.

← Back