Researchers Matias P. Gonzalez and Roberto A. Lineros from the Universidad de Santiago de Chile have recently published a study in the Journal of Cosmology and Astroparticle Physics that explores the dynamics of Weakly Interacting Massive Particle (WIMP) freeze-out using Tsallis nonextensive statistics. This research delves into the behavior of dark matter candidates and their interactions, which could have significant implications for our understanding of the universe’s energy composition.
The study generalizes the traditional thermal WIMP freeze-out process by incorporating Tsallis nonextensive statistics, a framework that allows for a more nuanced description of complex systems. The researchers computed various thermodynamic quantities, such as number and energy densities, pressure, entropy density, and the Hubble rate, using Curado-Tsallis q-distributions. These distributions are a generalization of the standard Boltzmann distribution, which is typically used in such calculations.
The Boltzmann equation was also generalized to obtain the comoving abundance and relic density of a dark-matter candidate, χ, in a model-independent setup. The thermally averaged cross section was expanded up to p-wave, and the freeze-out parameter x_f(q) was determined using a q-logarithmic inversion. The expansion rate was modified through ultra-relativistic rescalings of the effective relativistic degrees of freedom.
The researchers found that the freeze-out parameter x_f increases with q, and that QCD-threshold features propagate into the comoving abundance and relic density. They performed two q-grid scans: one fixing the thermally averaged cross section while varying the dark-matter mass, and another fixing the dark-matter mass while varying the s-wave coefficient. In both cases, they found a clear degeneracy in the preferred nonextensive parameter q_best along valleys in parameter space.
The study concludes that fixed-mass scans, which vary the thermally averaged cross section, are significantly more constraining than fixed-cross-section scans. This reflects that the relic density is mainly controlled by the thermally averaged cross section, so that for realistic cross sections, the best-fit q_best remains close to the extensive limit q→1.
While this research is primarily theoretical and does not directly impact the energy industry, it contributes to our broader understanding of dark matter and its interactions. This knowledge is crucial for developing accurate models of the universe’s energy composition, which could indirectly influence energy-related research and technologies in the future.
This article is based on research available at arXiv.