Infrared Quantum Electrodynamics and the Rayleigh‐Jeans Physics

ABSTRACT Infrared quantum electrodynamics (IR–QED) acquires a natural geometric interpretation once soft photons are described as adiabatically transported electron–photon clouds. Within this framework, the relevant infrared structure is encoded in a functional Berry phase associated with the space of gauge connections, and the corresponding Berry corrections modify the Rayleigh–Jeans spectrum. The infrared scaling symmetry of the Rayleigh–Jeans law leads to a simple renormalization–group equation whose solution determines the frequency dependence of an effective factor controlling the strength of the electron–photon cloud dressing. As a result, the energy density of the cosmic microwave background (CMB) receives a Berry‐induced correction that scales as a power law and produces a frequency‐dependent temperature excess in the radio domain. Although the exponent governing this scaling behavior is not fixed internally by the present formulation of IR–QED and must instead be determined phenomenologically, the existence and structure of the excess are genuine predictions of the theory. Remarkably, the resulting expression is extremely simple and naturally aligns with the deviations suggested by the ARCADE 2 data. Taken together, these results indicate that Berry phases in IR–QED may lead to observable consequences in the low‐frequency tail of the CMB spectrum.