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Atomic Nuclei: Nuclear Relaxation Processes01:23

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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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Updated: Nov 30, 2025

Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement
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Relieving the Hubble Tension with Primordial Magnetic Fields.

Karsten Jedamzik1, Levon Pogosian2,3

  • 1Laboratoire de Univers et Particules de Montpellier, UMR5299-CNRS, Universite de Montpellier, 34095 Montpellier, France.

Physical Review Letters
|November 16, 2020
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Summary

Primordial magnetic fields may resolve cosmological tensions. Accounting for baryon density inhomogeneities, induced by these fields, reconciles the Hubble constant and matter density measurements from Planck and supernovae data.

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Area of Science:

  • Cosmology
  • Astrophysics
  • Particle Physics

Background:

  • Cosmic Microwave Background (CMB) measurements from Planck indicate a Hubble constant (H₀) significantly lower than that from Type Ia supernovae.
  • The standard cosmological model, when fitted to Planck data, predicts higher matter density (Ωm) and clustering amplitude (S₈) than observed in Dark Energy Survey Year 1 data.
  • These discrepancies, known as the H₀ and S₈-Ωm tensions, challenge the current understanding of the universe.

Purpose of the Study:

  • To investigate whether enhanced recombination rates due to small-scale baryon density inhomogeneities can resolve the H₀ and S₈-Ωm tensions.
  • To explore the role of primordial magnetic fields in inducing these baryon inhomogeneities.
  • To determine if the magnetic field strength required to resolve cosmological tensions is consistent with observed astrophysical magnetic fields.

Main Methods:

  • Incorporating an enhanced recombination rate into cosmological models.
  • Analyzing the impact of baryon density inhomogeneities on CMB and large-scale structure observables.
  • Comparing model predictions with observational data from Planck, Type Ia supernovae, and the Dark Energy Survey.

Main Results:

  • Accounting for enhanced recombination rates due to baryon inhomogeneities successfully resolves both the H₀ and S₈-Ωm tensions.
  • The required baryon inhomogeneities can be generated by primordial magnetic fields present before recombination.
  • The magnetic field strength needed to resolve these tensions aligns with values required to explain galactic, cluster, and extragalactic magnetic fields without dynamo amplification.

Conclusions:

  • Primordial magnetic fields offer a compelling solution to major cosmological tensions.
  • The proposed mechanism provides a unified explanation for both H₀ and S₈-Ωm discrepancies.
  • Further research into primordial magnetic fields is warranted, with specific observational targets identified.