2025/11/20 by Gonzalez, Matias P., Lineros, Roberto A.
Physics and Astronomy · #Cosmology and Gravitation Theories #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #Pulsars and Gravitational Waves Research #Statistical Mechanics and Entropy
paper · doi:10.48550/arxiv.2511.16487
openalex publication_date 2025/11/20 · openalex created_date 2025/11/23 · openalex updated_date 2026/07/28
We generalize thermal WIMP (Weakly Interacting Massive Particle) freeze-out within Tsallis nonextensive statistics. Using Curado-Tsallis q-distributions fq(E;μ,T) we compute q-deformed number and energy densities, pressure, entropy density and Hubble rate, \nq,ρq,Pq,sq,Hq\. The Boltzmann equation is generalized accordingly to obtain the comoving abundance Yχ,q(x) and relic density Ωχ,qh2 for a dark-matter candidate χ in a model-independent setup. The thermally averaged cross section is expanded as ⟨σv⟩q ≈ a + b ⟨ v\rm rel2⟩q up to p-wave. The freeze-out parameter xf(q) is determined from Γ_\rm ann,q(Tf)≃ Hq(Tf) using a q-logarithmic inversion, with the expansion rate modified through ultra-relativistic rescalings Rρ(q) of the effective relativistic degrees of freedom g_* and g*s. We show that xf increases with q and that QCD-threshold features propagate into Yχ,q(x) and Ωχ,qh2. We then perform two q-grid scans: fixing ⟨σv⟩q while varying the dark-matter mass mχ, and fixing mχ while varying the s-wave coefficient a. For an s-wave dominated scenario we construct χ2 profiles in these planes by comparing Ωχ,qh2 with the Planck benchmark Ωc h2 = 0.120± 0.001. In both cases we find a clear degeneracy in the preferred nonextensive parameter q\rm best along valleys in parameter space. However, fixed-mass scans (varying ⟨σv⟩q) are significantly more constraining than fixed-cross-section scans, reflecting that Ωχ,qh2 is mainly controlled by ⟨σv⟩q, so that for realistic cross sections the best-fit q\rm best remains close to the extensive limit q→ 1.