Model-independent curvature determination with 21cm intensity mapping experiments

TL;DR

Upcoming 21cm intensity mapping experiments like HIRAX can achieve model-independent measurements of the Universe's spatial curvature at percent-level accuracy, overcoming degeneracies with dark energy assumptions.

Contribution

The paper demonstrates that 21cm intensity mapping experiments can significantly improve model-independent curvature constraints, even with arbitrary dark energy equations of state.

Findings

HIRAX can improve curvature constraints by about an order of magnitude.

Model-independent methods effectively break degeneracies between dark energy and curvature.

Sample variance limit is an order of magnitude better than forecasted constraints.

Abstract

Recent precision cosmological parameter constraints imply that the spatial curvature of the Universe is essentially dynamically negligible - but only if relatively strong assumptions are made about the equation of state of dark energy (DE). When these assumptions are relaxed, strong degeneracies arise that make it hard to disentangle DE and curvature, degrading the constraints. We show that forthcoming 21cm intensity mapping experiments such as HIRAX are ideally designed to carry out model-independent curvature measurements, as they can measure the clustering signal at high redshift with sufficient precision to break many of the degeneracies. We consider two different model-independent methods, based on `avoiding' the DE-dominated regime and non-parametric modelling of the DE equation of state respectively. Our forecasts show that HIRAX will be able to improve upon current model-independent constraints by around an order of magnitude, reaching percent-level accuracy even when an arbitrary DE equation of state is assumed. In the same model-independent analysis, the sample variance limit for a similar survey is another order of magnitude better.