Neutrino mass without cosmic variance

TL;DR

This paper explores how measurements of scale-dependent halo bias and growth rate from galaxy surveys can constrain neutrino mass without cosmic variance, highlighting the potential and challenges of this approach.

Contribution

It introduces forecasts for neutrino mass constraints using galaxy and lensing statistics sensitive to scale-dependent bias and growth rate, emphasizing the benefits of multi-tracer techniques.

Findings

High tracer density improves neutrino mass constraints.

Multi-tracer methods can beat cosmic variance limits.

Scale-dependent bias offers a new probe of neutrino effects.

Abstract

Measuring the absolute scale of the neutrino masses is one of the most exciting opportunities available with near-term cosmological datasets. Two quantities that are sensitive to neutrino mass, scale-dependent halo bias $b(k)$ and the linear growth parameter $f(k)$ inferred from redshift-space distortions, can be measured without cosmic variance. Unlike the amplitude of the matter power spectrum, which always has a finite error, the error on $b(k)$ and $f(k)$ continues to decrease as the number density of tracers increases. This paper presents forecasts for statistics of galaxy and lensing fields that are sensitive to neutrino mass via $b(k)$ and $f(k)$. The constraints on neutrino mass from the auto- and cross-power spectra of spectroscopic and photometric galaxy samples are weakened by scale-dependent bias unless a very high density of tracers is available. In the high density limit, using multiple tracers allows cosmic-variance to be beaten and the forecasted errors on neutrino mass shrink dramatically. In practice, beating the cosmic variance errors on neutrino mass with $b(k)$ will be a challenge, but this signal is nevertheless a new probe of neutrino effects on structure formation that is interesting in its own right.