Photon gas at the Planck scale within the doubly special relativity

Within the approach to doubly special relativity (DSR) suggested by Magueijo and Smolin, a new algebraically justified rule of so-called κ-addition for the energies of identical particles is proposed. This rule permits to introduce the nonlinear κ-dependent Hamiltonian for one-mode multi-photon (sub)system. On its base, with different modes treated as independent, the thermodynamics of black-body radiation is explored within DSR, and main thermodynamic quantities are obtained. In their derivation, we use both the analytical tools within mean field approximation (MFA) and numerical evaluations based on exact formulas. The entropy of one-mode subsystem turns out to be finite (bounded). Another unusual result is the existence of threshold temperature above which radiation is present. Specific features of the obtained results are explained and illustrated with a number of plots. Comparison with some works of relevance is given. •Doubly special relativity implies restricting of particle four-momentum by the Planck scale.•Certain new κ-addition rule for the four-momenta of (identical) particles is proposed.•Usage of κ-addition for monochromatic photons induces supplementary attraction.•Thermodynamics of black-body radiation of κ-photons demonstrates new effects.•A kind of threshold temperature of black-body radiation of κ-photons does appear.