Dark Energy: From Brake to Engine ⚡ экспресс
We present the Ph-ΛsCDM model—an implementation of the sign-switching cosmological constant (ΛsCDM) concept using a phantom scalar field within general relativity. The phantom field, with a kinetic term of the wrong sign, evolves on a bounded potential of hyperbolic tangent type, causing a smooth transition from a regime with negative dark energy density (analogous to anti-de Sitter) to positive (de Sitter) in the late Universe. The negative kinetic term, usually considered a pathology, here serves as a mechanism to lift the field from a vacuum state with negative energy to one with positive energy. We show that the field can create repulsion even when its energy density is still negative. Yet the cosmology remains under control: the total energy is positive, the late-time attractor is a de Sitter space without a Big Rip, and the dynamics are limited to the infrared regime. The model provides a concrete mechanism to address a number of cosmological tensions.
The universe is expanding faster and faster thanks to dark energy. But measurements of the rate give contradictory results. A new explanation: in the past, dark energy acted as a brake, slowing the galaxies' recession, and then switched to acceleration. Like a car that first rolls backward and then lunges forward. This transition is described by the Ph-ΛsCDM model, based on the theory of gravity by Einstein. It uses a phantom field — a substance capable of smoothly changing the sign of energy from attraction to repulsion. This avoids the 'Big Rip' that previous theories threatened. This is a development of ideas that emerged after the discovery of acceleration by Perlmutter. Most unexpectedly, the field starts accelerating even while the energy is still attracting — as if the engine started working before the clutch engaged. The model promises a stable future despite the grim predictions of standard cosmology.
🎯 Phantom energy is so named for its ability to violate physical laws, like a ghost passing through walls.