Differentiating CDM and Baryon Isocurvature Models with 21 cm Fluctuations

TL;DR

This paper explores how future 21 cm fluctuation observations can distinguish between CDM and baryon isocurvature models, which are indistinguishable by CMB power spectra alone, especially with large blue-tilted spectra.

Contribution

It demonstrates that 21 cm surveys can effectively differentiate CDM and baryon isocurvature modes by analyzing their distinct evolution patterns.

Findings

21 cm fluctuations can distinguish CDM and baryon isocurvature modes.

Large blue-tilted spectra enhance the detectability of differences.

Future surveys have potential to discriminate these models effectively.

Abstract

We discuss how one can discriminate models with cold dark matter (CDM) and baryon isocurvature fluctuations. Although current observations such as cosmic microwave background (CMB) can severely constrain the fraction of such isocurvature modes in the total density fluctuations, CMB cannot differentiate CDM and baryon modes by the shape of its power spectra. However, the evolution of CDM and baryon density fluctuations are different for each model, thus it would be possible to discriminate those isocurvature modes by extracting information on the fluctuations of CDM/baryon itself. We discuss that observations of 21 cm fluctuations can in principle differentiate these modes and demonstrate to what extent we can distinguish them with future 21 cm surveys. We show that, when the isocurvature mode has a large blue-tilted initial spectrum, 21 cm survey can clearly probe the difference.