The Infraparticle Edge
Why charged particles don't have sharp energy edges in quantum physics
When charged particles emit photons, they don't have a single well-defined energy boundary—instead they fade out gradually at the edge, following a mathematical power law. Rey shows this fuzzy edge comes directly from soft photons we can't measure individually, and that the exact shape of this edge encodes information about how those unmeasured photons behave.
Particle detectors can only measure particles down to a minimum energy threshold—softer photons get lost. Understanding how this measurement limit shapes what we observe at the edge of energy spectra is essential for extracting accurate particle properties from real experiments and for theoretical predictions in high-energy physics.