Speaker
Description
The recent baryon acoustic oscillation (BAO) measurements from the DESI collaboration have revealed a first hint towards a deviation from a cosmological constant, signaling a preference for dynamical dark energy. In this talk, we explore the deep theoretical implications of these observations for dark energy and gravitational physics. Utilizing a model-agnostic, non-parametric reconstruction approach, we constrain the behaviour of the dark energy equation of state. Our analysis demonstrates that the combined DESI, CMB, and Type Ia Supernovae datasets favor a crossing of the phantom divide, a behavior that structurally rules out standard canonical scalar field models like quintessence due to ghost instabilities.
To interpret this result, we survey the wider scalar-tensor landscape via the Effective Field Theory of Dark Energy, within the Horndeski class of gravity theories. We identify the non-minimal coupling of gravity as the unique operator capable of stabilizing this phantom crossing, establishing the DESI results as a potential observational hint of modified gravity.