Reconnection-Driven Injection and Stochastic Reacceleration during Cosmological Magnetogenesis
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arXiv
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| Format: | Preprint |
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2026
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| author | Ha, Ji-Hoon |
| author_facet | Ha, Ji-Hoon |
| contents | We investigate whether magnetic reconnection can provide suprathermal proton seed particles during cosmological magnetogenesis prior to nonlinear structure formation. Previous work showed that pressure-anisotropy-driven stochastic acceleration alone is strongly limited by cosmological expansion and Coulomb cooling. Here, we extend this framework by adding a phenomenological reconnection-driven source term to the Fokker--Planck equation for the isotropic ion distribution, with the injection power tied to the magnetic-energy growth rate during magnetogenesis. We find that reconnection can act as a fast injection channel and can produce a visible suprathermal tail. However, the resulting nonthermal energy fraction remains very small, of order $10^{-7}$ in the fiducial model, implying a negligible nonthermal pressure contribution to the pre-structure intergalactic medium. This limitation arises because the extremely high-beta plasma contains only a small magnetic-energy reservoir, even when reconnection itself is locally fast. Using a test-particle shock reacceleration estimate, we further show that the reconnection-produced tail can enhance the suprathermal proton population available for later structure-formation shocks by about an order of magnitude. Nevertheless, the associated hadronic gamma-ray emission from low-density cluster outskirts is expected to remain far below current detectability. We therefore conclude that reconnection during cosmological magnetogenesis is unlikely to dominate the cosmic-ray energy budget directly, but may provide a low-level seed population for subsequent shock acceleration. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2606_01775 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Reconnection-Driven Injection and Stochastic Reacceleration during Cosmological Magnetogenesis Ha, Ji-Hoon High Energy Astrophysical Phenomena Cosmology and Nongalactic Astrophysics We investigate whether magnetic reconnection can provide suprathermal proton seed particles during cosmological magnetogenesis prior to nonlinear structure formation. Previous work showed that pressure-anisotropy-driven stochastic acceleration alone is strongly limited by cosmological expansion and Coulomb cooling. Here, we extend this framework by adding a phenomenological reconnection-driven source term to the Fokker--Planck equation for the isotropic ion distribution, with the injection power tied to the magnetic-energy growth rate during magnetogenesis. We find that reconnection can act as a fast injection channel and can produce a visible suprathermal tail. However, the resulting nonthermal energy fraction remains very small, of order $10^{-7}$ in the fiducial model, implying a negligible nonthermal pressure contribution to the pre-structure intergalactic medium. This limitation arises because the extremely high-beta plasma contains only a small magnetic-energy reservoir, even when reconnection itself is locally fast. Using a test-particle shock reacceleration estimate, we further show that the reconnection-produced tail can enhance the suprathermal proton population available for later structure-formation shocks by about an order of magnitude. Nevertheless, the associated hadronic gamma-ray emission from low-density cluster outskirts is expected to remain far below current detectability. We therefore conclude that reconnection during cosmological magnetogenesis is unlikely to dominate the cosmic-ray energy budget directly, but may provide a low-level seed population for subsequent shock acceleration. |
| title | Reconnection-Driven Injection and Stochastic Reacceleration during Cosmological Magnetogenesis |
| topic | High Energy Astrophysical Phenomena Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2606.01775 |