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| Main Authors: | , , , |
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| Format: | Preprint |
| Published: |
2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2604.24835 |
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Table of Contents:
- Primordial magnetic fields (PMFs) enhance small-scale structure formation through the Lorentz force acting on baryons, boosting the abundance of low-mass halos and their hosted galaxies. We show that the reionisation history calibrated with the UV luminosity function (UVLF) provides stringent bounds: strong PMFs induce a characteristic double reionisation at $z \approx 24$ that is incompatible with CMB measurements of the optical depth, yielding $\sqrt{\left\langle B^2 \right\rangle} < 0.27\,{\rm nG}$ and $< 0.18\,{\rm nG}$ for $n_B = -2$ and $n_B = 2$ respectively at $95\%\,{\rm CL}$ using Planck priors on $τ$. This establishes early galaxy observables as among the most sensitive probes of PMFs in Gaussian, non-helical scenarios.