Cosmological Limits on the Neutrino Mass from theLyαForest

The $\mathrm{Ly}\alpha$ forest in quasar spectra probes scales where massive neutrinos can strongly suppress the growth of mass fluctuations. Using hydrodynamic simulations with massive neutrinos, we successfully test techniques developed to measure the mass power spectrum from the forest. A recent observational measurement in conjunction with a conservative implementation of other cosmological constraints places upper limits on the neutrino mass: $m_{\nu }<5.5\mathrm{}\mathrm{eV}$ for all values of ${\Omega }_m$, and $m_{\nu }\lesssim 2.4({\Omega }_m/0.17-1)\mathrm{eV}$, if $0.2\le {\Omega }_m\le 0.5$ as currently observationally favored (both $95\%$ C.L.).