What question did this study set out to answer?

The aim is to explore how the cosmic microwave background spectrum can impose limits on the mass of photons.

February 2, 2026Open Access

Thermodynamic Constraints on Photon Mass from the CMB Blackbody Spectrum

Key Points

The aim is to explore how the cosmic microwave background spectrum can impose limits on the mass of photons.
Modified the photon dispersion relation
Compared deviations with COBE/FIRAS and Planck 2018 data
Derived an upper bound on photon mass
Identified a potential upper limit for photon mass
Showed spectral deformation compatible with effective Generalized Inverse Gaussian representation
Demonstrated CMB thermodynamics' sensitivity to small deviations from gauge invariance

Abstract

This preprint investigates thermodynamic constraints on a finite photon mass using deviations from the cosmic microwave background (CMB) blackbody spectrum. By modifying the photon dispersion relation and comparing with COBE/FIRAS and Planck 2018 data, an upper bound on the photon mass is derived. The resulting spectral deformation is shown to admit an effective Generalized Inverse Gaussian (GIG) representation, highlighting the sensitivity of CMB thermodynamics to extremely small departures from exact gauge invariance.

Thermodynamic Constraints on Photon Mass from the CMB Blackbody Spectrum

Key Points

Abstract

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