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Can WIMPs Survive a Magnetized Early Universe?
by Malcolm Fairbairn, María Olalla Olea-Romacho, Pranjal Ralegankar
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Submission summary
| Authors (as registered SciPost users): | Maria Olalla Olea Romacho |
| Submission information | |
|---|---|
| Preprint Link: | https://arxiv.org/abs/2507.18692v1 (pdf) |
| Date submitted: | Aug. 11, 2025, 10:26 p.m. |
| Submitted by: | Maria Olalla Olea Romacho |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approach: | Phenomenological |
Abstract
Primordial magnetic fields (PMFs) can seed additional small-scale matter fluctuations, leading to the formation of dense, early-collapsing dark matter structures known as minihalos. These minihalos may dramatically amplify the dark matter annihilation signal if dark matter is composed of self-annihilating thermal relic particles such as WIMPs. In this work, we explore the viability of this scenario by analysing the annihilation signal from minihalos with prompt central cusps, $\rho \propto r^{-3/2}$, formed due to the enhanced power spectrum induced by PMFs. Using observational constraints from the Virgo cluster and incorporating benchmark values for the magnetic field strength motivated by cosmological phase transitions such as the electroweak and QCD phase transitions, as well as the best-fit value from DESI and Planck data, we derive constraints on the dark matter annihilation cross section. We find that large portions of the WIMP parameter space are excluded, and magnetic fields produced during phase transitions with temperatures $T \lesssim 100 \, \rm{GeV}$ disfavour dark matter masses below $400 \, \rm{GeV}$. Notably, magnetic fields generated at or below the QCD phase transition scale, or with amplitudes favored by current cosmological data, are in strong tension with self-annihilating WIMPs across a wide mass range extending beyond the $\mathrm{TeV}$ scale. Our results establish indirect detection as a sensitive probe of the interplay between early-universe magnetogenesis and the microphysics of dark matter.
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- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
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This work is interesting as it connects topics in several different subfields. I have a few comments.
The current draft lacks a detailed discussion of how the authors incorporate the effect of primordial magnetic fields in their calculation. Presumably, this is based on the results of Ralegankar et al. (Ref. [60]). In the current draft, there is only a brief quantitative discussion in the second paragraph of Section III. Since this is the major point of the paper, a more quantitative discussion with technical details is needed.
Related to the previous point, they should provide more details on how they obtain the results in Figure 3.
Figure 3 shows the benchmark case for generating primordial magnetic fields at the electroweak phase transition. However, this is the least illustrative case among the three benchmark scenarios, since the relevant effect is minor. Why not include the other two cases in Figure 3 for comparison? That would help readers better understand the impact of different generation scenarios and highlight the significance of this work.
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Please find attached our detailed response to the referee report (see file answer1.pdf).
Author: Maria Olalla Olea Romacho on 2025-10-27 [id 5958]
(in reply to Report 2 on 2025-09-29)Please find attached our detailed response to the referee report (see file answer2.pdf).
Attachment:
answer2.pdf