Constraining massive neutrinos using cosmological 21 cm observations

TL;DR

The paper investigates constraining neutrino masses using cosmology with 21 cm fluctuations from the epoch of reionization. By employing a Fisher matrix framework that combines Planck-like CMB data, galaxy surveys, and 21 cm observations across several instrument designs, it forecasts how neutrino mass constraints improve with smaller scales and larger survey volumes. The results indicate that 21 cm data, especially from a FFTT-class instrument, could achieve $\sigma_{M_\nu}$ near $0.01$ eV and potentially reveal the mass hierarchy, while SKA-like data with Planck could reach $\sim0.16$ eV, enabling a ~2σ detection for plausible masses. These findings suggest 21 cm cosmology as a promising, though technically challenging, path to enhancing our understanding of neutrino masses and their hierarchy in the Universe.

Abstract

Observations of neutrino oscillations show that neutrinos have mass. However, the best constraints on this mass currently come from cosmology, via measurements of the cosmic microwave background and large scale structure. In this paper, we explore the prospects for using low-frequency radio observations of the redshifted 21 cm signal from the epoch of reionization to further constrain neutrino masses. We use the Fisher matrix formalism to compare future galaxy surveys and 21 cm experiments. We show that by pushing to smaller scales and probing a considerably larger volume 21 cm experiments can provide stronger constraints on neutrino masses than even very large galaxy surveys. Finally, we consider the possibility of going beyond measurements of the total neutrino mass to constraining the mass hierarchies. For a futuristic, 21 cm experiment we show that individual neutrino masses could be measured separately from the total neutrino mass.

Figures (7)

• Figure 1: Effect of a different neutrino mass on the power spectrum at redshifts $z=0.3$ (solid curve), 4 (dashed curve), and 8 (dotted curve). The curves represent the derivatives of the matter power spectrum with respect to neutrino mass for a fiducial mass value of $M_\nu=0.3\hbox{eV}$. The vertical dashed lines represent the non-linear scale at redshifts $z=0.3$, 4, and 8 (from left to right). Note that the derivative becomes more negative at lower redshifts, as massive neutrinos have more time to affect the power spectrum.
• Figure 2: Difference between the power spectra between the normal and inverted hierarchy at different redshifts. We plot the ratio of the power spectrum calculated with total neutrino mass $M_\nu=0.12$ distributed in the normal hierarchy (dotted curve) and inverted hierarchy (solid curve) relative to the case where the three neutrino masses are degenerate ($m_1=m_2=m_3$). These curves are calculated at $z=0$ (thin curves) and $z=8$ (thick curves). The difference continues to smaller scales, but saturates at $\sim0.2 \%$ at $k=1 h {\rm Mpc}^{-1}$.
• Figure 3: Comparison of angle averaged effective volume for galaxy and 21 cm surveys. SDSS (thin solid curve), G1 (thin dotted curve), G2 (thin short dashed curve), G3 (thin long dashed curve), MWA (thick solid curve), SKA (thick dotted curve), and FFTT (thick dashed curve).
• Figure 4: 2$\sigma$ constraints on $M_\nu$ (solid curve) from SKA+PLANCK (dotted curve) and FFTT+PLANCK (dashed curve) for the normal (thin curves) and inverted (thick curves) hierarchies.
• Figure 5: 68-% confidence ellipses in the $M_\nu-w$ plane from PLANCK in combination with SDSS (thin dotted), G2 (thin short dashed), G1 (thin solid), G3 (thin long dashed), MWA (thick dotted), SKA (thick dashed), and FFTT (thick solid).