Strong bound on canonical ultra-light axion dark matter from the
  Lyman-alpha forest
  We present a new bound on the ultra-light axion (ULA) dark matter mass
$m_\text{a}$, using the Lyman-alpha forest to look for suppressed cosmic
structure growth: a 95% lower limit $m_\text{a} > 2 \times
10^{-20}\,\text{eV}$. This strongly disfavors ($> 99.7\%$ credibility) the
canonical ULA with $10^{-22}\,\text{eV} < m_\text{a} < 10^{-21}\,\text{eV}$,
motivated by the string axiverse and solutions to possible tensions in the cold
dark matter model. We strengthen previous equivalent bounds by about an order
of magnitude. We demonstrate the robustness of our results using an optimized
emulator of improved hydrodynamical simulations.
