# Strong bound on canonical ultra-light axion dark matter from the Lyman-alpha forest

**Authors:** Keir K. Rogers, Hiranya V. Peiris  
**arXiv:** [2007.12705](https://arxiv.org/abs/2007.12705)  
**Date:** 2020-07-24  
**Summary page:** https://www.summarizepaper.com/en/paper/2007.12705v1/

## Key points

- Keir K. Rogers and Hiranya V. Peiris present a new bound on the mass of ultra-light axion (ULA) dark matter using the Lyman-alpha forest to look for suppressed cosmic structure growth.
- The authors report a 95% lower limit of $m_\text{a} > 2 \times 10^{-20}\,\text{eV}$, which strongly disfavors the canonical ULA with $10^{-22}\,\text{eV} < m_\text{a} < 10^{-21}\,\text{eV}$ at over 99.7% credibility.
- The authors strengthen previous equivalent bounds by about an order of magnitude, demonstrating the robustness of their results using an optimized emulator based on improved hydrodynamical simulations.
- The Lyman-alpha forest is a powerful tool for probing cosmological structures at high redshifts, making it well suited for studying dark matter candidates like ULAs.
- ULAs are a promising candidate for explaining some long-standing problems in cosmology but this work suggests that they may not be as viable as previously thought.
- This study has important implications for our understanding of dark matter and its properties.
- Further research will be needed to confirm these findings and explore other potential explanations for dark matter's nature and behavior.

## Summary

In a recent study, Keir K. Rogers and Hiranya V. Peiris present a new bound on the mass of ultra-light axion (ULA) dark matter using the Lyman-alpha forest to look for suppressed cosmic structure growth. The authors report a 95% lower limit of $m_\text{a} > 2 \times 10^{-20}\,\text{eV}$, which strongly disfavors the canonical ULA with $10^{-22}\,\text{eV} < m_\text{a} < 10^{-21}\,\text{eV}$ at over 99.7% credibility. This canonical ULA is motivated by the string axiverse and solutions to possible tensions in the cold dark matter model. The authors strengthen previous equivalent bounds by about an order of magnitude, demonstrating the robustness of their results using an optimized emulator based on improved hydrodynamical simulations. The Lyman-alpha forest is a powerful tool for probing cosmological structures at high redshifts, making it well suited for studying dark matter candidates like ULAs. This study has important implications for our understanding of dark matter and its properties. ULAs are a promising candidate for explaining some long-standing problems in cosmology but this work suggests that they may not be as viable as previously thought. Further research will be needed to confirm these findings and explore other potential explanations for dark matter's nature and behavior. Overall, this study represents an important step forward in our quest to understand one of the most fundamental mysteries of the universe: what is dark matter made of? By placing new constraints on ULAs, it brings us closer to answering this question and unlocking some of the deepest secrets of our cosmos.