Cosmological cancellation of the vacuum energy density

Understand

We propose a simple model that provides a dynamical cancellation mechanism of the vacuum energy density appearing either in the form of a bare cosmological constant, quantum fluctuations of matter fields or the result of phase transitions.

• This `conformal compensator model' is based on a conformal coupling $A(\varphi)$ between the Einstein and the Jordan frames.
• This couples a second scalar field $\lambda$ to the trace of the matter energy-momentum tensor, including the bare cosmological constant, and serves as a dynamical Lagrange multiplier.
• As a result, the scalar $\lambda$ relaxes to a value which cancels the contributions from the vacuum energy density to the Friedmann equation, and adjusts itself to changes of the vacuum energy density after matter phase transitions.