Understand
Most efforts to detect signatures of dynamical dark energy are focused on late times, $z \lesssim 2$, where the dark energy component begins to dominate the cosmic energy density.
- Many theoretical models involving dynamical dark energy exhibit a 'freezing' equation of state however, where $w \to -1$ at late times, with a transition to a 'tracking' behaviour at earlier times (with $w \gg -1$ at sufficiently high redshift).
- In this paper, we study whether large-scale structure surveys in the post-reionisation matter-dominated regime, $2 \lesssim z \lesssim 6$, are sensitive to this behaviour, on the basis that the dark energy component should remain detectable (despite being strongly subdominant) in this redshift range given sufficiently precise observations.
- Using phenomenological models inspired by parameter space studies of Horndeski (generalised scalar-tensor) theories, we show how existing CMB and large-scale structure measurements constrain the dark energy equation of state in the matter-dominated era, and examine how forthcoming galaxy surveys and 21cm intensity mapping instruments can improve constraints in this regime.