# Constraining sterile neutrino cosmologies with strong gravitational lensing observations at redshift z~0.2

**Authors:** S. Vegetti, G. Despali, M. R. Lovell, W. Enzi  
**arXiv:** [1801.01505](https://arxiv.org/abs/1801.01505)  
**Date:** 2018-01-04  
**Summary page:** https://www.summarizepaper.com/en/paper/1801.01505v2/

## Key points

- Utilize data from the Sloan Lens ACS Survey
- Investigate free-streaming properties of dark matter particles
- Focus on a sample of 11 gravitational lens systems
- Analyze observed amount of subhaloes and line-of-sight dark matter haloes within these systems
- Combine detection of small-mass dark matter halo reported by Vegetti et al. in 2010 with non-detections reported by Vegetti et al. in 2014
- Compare derived subhalo and halo mass functions with expectations from cold dark matter (CDM) and resonantly produced sterile neutrino models
- Constrain half-mode mass to be $\log M_{\rm{hm}} \left[M_\odot\right] < 12.0$ (equivalent thermal relic mass $m_{\rm th} > 0.3$ keV) at a significance level of 2$\sigma$
- Exclude sterile neutrino models with neutrino masses $m_{\rm s} < 0.8$ keV for any value of $L_{\rm 6}$
- Constraints are weaker compared to other methods such as observations of Milky Way satellites, measurements of the 3.5 keV X-ray line, and studies of the Lyman $\alpha$ forest
- Constraints are more robust as they are less affected by baryonic processes and do not rely on assumptions about thermal histories for intergalactic medium
- Higher data quality, source, and lens redshifts required for tighter constraints in future studies

## Summary

In this study, the authors utilize data from the Sloan Lens ACS Survey to investigate the free-streaming properties of dark matter particles. They focus on a sample of 11 gravitational lens systems and analyze the observed amount of subhaloes and line-of-sight dark matter haloes within these systems. The researchers combine the detection of a small-mass dark matter halo reported by Vegetti et al. in 2010 with non-detections reported by Vegetti et al. in 2014. By comparing the derived subhalo and halo mass functions with expectations from cold dark matter (CDM) and resonantly produced sterile neutrino models, they aim to constrain the half-mode mass, which represents the mass scale at which the linear matter power spectrum is reduced by 50% relative to the CDM model. Their analysis leads them to constrain the half-mode mass to be $\log M_{\rm{hm}} \left[M_\odot\right] < 12.0$ (equivalent thermal relic mass $m_{\rm th} > 0.3$ keV) at a significance level of 2$\sigma$. This constraint excludes sterile neutrino models with neutrino masses $m_{\rm s} < 0.8$ keV for any value of $L_{\rm 6}$. The authors acknowledge that their constraints are weaker compared to those provided by other methods such as observations of Milky Way satellites, measurements of the 3.5 keV X-ray line, and studies of the Lyman $\alpha$ forest. However, they argue that their constraints are more robust as they are less affected by baryonic processes and do not rely on assumptions about thermal histories for intergalactic medium. To obtain tighter constraints in future studies, higher data quality as well as higher source and lens redshifts will be required. Overall, this research contributes significantly to our understanding of free-streaming properties of dark matter particles and provides valuable insights into sterile neutrino cosmologies at a redshift around 0.2.