Decoherence Can Relax Cosmic Acceleration
  In this work we investigate the semi-classical backreaction for a quantised
conformal scalar field and classical vacuum energy. In contrast to the usual
approximation of a closed system, our analysis includes an environmental sector
such that a quantum-to-classical transition can take place. We show that when
the system decoheres into a mixed state with particle number as the classical
observable de Sitter space is destabilized, which is observable as a gradually
decreasing Hubble rate. In particular we show that at late times this mechanism
can drive the curvature of the Universe to zero and has an interpretation as
the decay of the vacuum energy demonstrating that quantum effects can be
relevant for the fate of the Universe.
