Systematic errors in the measurement of neutrino masses due to baryonic
  feedback processes: Prospects for stage IV lensing surveys
  We examine the importance of baryonic feedback effects on the matter power
spectrum on small scales, and the implications for the precise measurement of
neutrino masses through gravitational weak lensing. Planned large galaxy
surveys such as the Large Synoptic Sky Telescope (LSST) and Euclid are expected
to measure the sum of neutrino masses to extremely high precision, sufficient
to detect non-zero neutrino masses even in the minimal mass normal hierarchy.
We show that weak lensing of galaxies while being a very good probe of neutrino
masses, is extremely sensitive to baryonic feedback processes. We use publicly
available results from the Overwhelmingly Large Simulations (OWLS) project to
investigate the effects of active galactic nuclei feedback, the nature of the
stellar initial mass function, and gas cooling rates, on the measured weak
lensing shear power spectrum. Using the Fisher matrix formalism and priors from
CMB+BAO data, we show that when one does not account for feedback, the measured
neutrino mass may be substantially larger or smaller than the true mass,
depending on the dominant feedback mechanism, with the mass error |\Delta m_nu|
often exceeding the mass m_nu itself. We also consider gravitational lensing of
the cosmic microwave background (CMB) and show that it is not sensitive to
baryonic feedback on scales l < 2000, although CMB experiments that aim for
sensitivities sigma(m_nu) < 0.02 eV will need to include baryonic effects in
modeling the CMB lensing potential. A combination of CMB lensing and galaxy
lensing can help break the degeneracy between neutrino masses and baryonic
feedback processes. We conclude that future large galaxy lensing surveys such
as LSST and Euclid can only measure neutrino masses accurately if the matter
power spectrum can be measured to similar accuracy.
