Weighing massive neutrinos with Lyman-α observations

Abstract

The presence of massive neutrinos has still not been revealedby the cosmological data. We considera novel method based on the two-point line-of-sight correlation function ofhigh-resolution Lyman-α data to achieve this end in the paper.We adopt semi-analytic models of Lyman-αclouds for the study. We employ Fisher matrix technique to show thatit is possible to achieve a scenario in whichthe covariance of the two-point function nearly vanishes for both the spectroscopic noise and the signal.We analyze this near `zero noise' outcome in detail to argue it might be possible to detect neutrinosof mass range m ν ≃ 0.05–0.1 eV with signal-to-noise of unity witha single QSO line of sight. We show that this estimate can be improved to SNR ≃ 3–6 with data along multiple line of sightswithin the redshift range z ≃ 2–2.5.Such data sets already exist in the literature.We further carry outprincipal component analysis of the Fisher matrix to study the degeneraciesof the neutrino mass with otherparameters. We show that Planck priors lift the degeneracies betweenthe neutrino mass and other cosmological parameters.However, the prospects of the detection of neutrino mass are driven by the poorly-determined parameters characterizing the ionization and thermal state of Lyman-α clouds. We have also mentioned the possible limitations andobservational challenges posed in measuring the neutrino mass using our method.