Probing dark energy using anisotropies in the clustering of post-EoR H i distribution

We propose an anisotropy quantifier of the H i 21-cm signal traditionally used to clock the astrophysics of the reionization era as a post-reionization dark energy diagnostic. We find that the anisotropy probe can be measured at SNR ∼ 10 in both auto-correlation and in cross-correlation with the Ly-α forest over a wide z and k-range. We propose to use the BAO signature on the anisotropy signal to measure ( H(z), DA(z)). Subsequently, we put constraints on a dark energy model involving a negative cosmological constant on top of a quintessence scalar field and find that such a model is consistent with futuristic observations.