Weighing Neutrinos: Weak Lensing Approach

TL;DR

Weak gravitational lensing can be used to measure neutrino mass by detecting suppression in the power spectrum, with future surveys potentially reaching sensitivities below current limits, depending on cosmological parameter accuracy.

Contribution

This paper demonstrates that weak lensing surveys can directly measure neutrino mass and explores the potential sensitivity of future surveys to lower neutrino mass limits.

Findings

A 100 sqr. degree survey can detect neutrino masses down to 3.5 eV.

An all-sky survey could reach 0.4 eV sensitivity with known cosmological parameters.

Small surveys may ignore neutrino effects unless combined with other parameter estimates.

Abstract

We study the possibility for a measurement of neutrino mass using weak gravitational lensing. The presence of non-zero mass neutrinos leads to a suppression of power at small scales and reduces the expected weak lensing signal. The measurement of such a suppression in the weak lensing power spectrum allows a direct measurement of the neutrino mass, in contrast to various other experiments which only allow mass splittings between two neutrino species. Making reasonable assumptions on the accuracy of cosmological parameters, we suggest that a weak lensing survey of 100 sqr. degrees can be easily used to detect neutrinos down to a mass limit of 3.5 eV at the 2 sigma level. This limit is lower than current limits on neutrino mass, such as from the Ly-alpha forest and SN1987A. An ultimate weak lensing survey of pi steradians down to a magnitude limit of 25 can be used to detect neutrinos down to a mass limit of 0.4 eV at the 2 sigma level, provided that other cosmological parameters will be known to an accuracy expected from cosmic microwave background spectrum using the MAP satellite. With improved parameters estimated from the PLANCK satellite, the limit on neutrino mass from weak lensing can be further lowered by another factor of 3 to 4. For much smaller surveys (10 sqr. degrees) that are likely to be first available in the near future with several wide-field cameras, the presence of neutrinos can be safely ignored when deriving conventional cosmological parameters such as the mass density of the Universe. However, armed with cosmological parameter estimates with other techniques, even such small area surveys allow a strong possibility to investigate the presence of non-zero mass neutrinos.