Evolution of primordial magnetic fields from phase transitions
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Bibliographic record
Abstract
We consider the evolution of primordial magnetic fields generated during cosmological, electroweak, or QCD phase transitions. We assume that the magnetic field generation can be described as an injection of magnetic energy to cosmological plasma at a given scale determined by the moment of magnetic field generation. A high Reynolds number ensures strong coupling between the magnetic field and fluid motions. The subsequent evolution of the magnetic field is governed by decaying hydromagnetic turbulence. Both our numerical simulations and a phenomenological description allow us to recover ``universal'' laws for the decay of magnetic energy and the growth of magnetic correlation length in the turbulent (low-viscosity) regime. In particular, we show that during the radiation-dominated epoch, the energy and correlation length of nonhelical magnetic fields scale as conformal time to the powers $\ensuremath{-}1/2$ and $+1/2$, respectively. For helical magnetic fields, the energy and correlation length scale as conformal time to the powers $\ensuremath{-}1/3$ and $+2/3$, respectively. The universal decay law of the magnetic field implies that the strength of the magnetic field generated during the QCD phase transition could reach $\ensuremath{\sim}{10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{G}$ with the present-day correlation length $\ensuremath{\sim}50\text{ }\text{ }\mathrm{kpc}$. The fields generated at the electroweak phase transition could be as strong as $\ensuremath{\sim}{10}^{\ensuremath{-}10}\text{ }\text{ }\mathrm{G}$ with correlation lengths reaching $\ensuremath{\sim}0.3\text{ }\text{ }\mathrm{kpc}$. These values of the magnetic fields are consistent with the lower bounds of the extragalactic magnetic fields.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it