Theory 04/Physics, Cosmos & Matter /Astroparticle
Cosmic Rays See a Horizon
Anisotropy is read as a source map. It may be a map of what we can see out to.
The anisotropy of PeV cosmic rays is set by a magnetic horizon imposed by the local void rather than by source distribution, so the arrival direction should track the void boundary.
01The evidence
Anisotropy at PeV energies is weak and does not align with plausible source populations, which suggests a propagation effect.
02The tension
Source models predict anisotropy from the distribution of accelerators, and they fail to reproduce the observed pattern.
03The mechanism
Charged particles diffuse, and diffusion has a horizon set by the scattering rate and the time available. Inside a void, the scattering rate is low and the horizon extends; outside, it truncates.
That makes the observed anisotropy a boundary effect, and predicts the arrival pattern should follow the void geometry rather than any source class.
04What this is not
Those models map sources. This maps the propagation boundary, which explains weak, misaligned anisotropy.
05Predictions
- P1Anisotropy should track the void boundary.
- P2The pattern should be energy-dependent through the horizon.
- P3Low-density sightlines should dominate.
06Refutation
Anisotropy aligning with known sources would restore the source map.
07What it changes
It would turn anisotropy into a local structure probe.