Gravitational dark matter: free streaming and phase space distribution

2021/12/29 by Md Riajul Haque, Debaprasad Maity, Haque, Md Riajul +1 · 4 citations
Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Cosmology and Gravitation Theories #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #Dark Matter and Cosmic Phenomena #FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc) #High Energy Physics - Phenomenology (hep-ph) #High Energy Physics - Theory (hep-th)

paper · pdf · doi:10.48550/arxiv.2112.14668

openalex publication_date 2021/12/29 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

Gravitational dark matter (DM) is the simplest possible scenario that has recently gained interest in the early universe cosmology. In this scenario, DM is assumed to be produced from the decaying inflaton through the gravitational interaction during reheating. Gravitational production from the radiation bath will be ignored as our analysis shows it to be suppressed for a wide range of reheating temperatures. Ignoring any other internal parameters except the DM mass and spin, a particular inflation model such as α-attractor, with a specific scalar spectral index (n_s) has been shown to uniquely fix the dark matter mass. For fermion type dark matter we found the mass m_f should be within (10⁴ - 10¹³) GeV, and for boson type DM, the mass m_s/X turned out to be within (10^-8-10¹³) GeV. Interestingly, if the inflaton equation of state ω_ϕ→ 1/3, the DM mass also approaches towards unique value, m_f ∼ 10¹⁰ GeV and m_s/X ∼ 10³ ( 8× 10³ ) GeV irrespective of the value of ω_ϕ. We further analyzed the phase space distribution (f_Y), and free streaming length (λ_fs) of these gravitationally produced DM. f_Y, which is believed to encode important information about DM, is shown to contain a characteristic primary peak at the initial time where the gravitational production is maximum for both fermion/boson. Apart from this fermionic phase-space distribution function contains an additional peak near the inflaton and fermion mass equality (m_Y=m_ϕ) arising for ω_ϕ>5/9. Since dark matter is produced during the reheating phase, gravitational instability forming small-scale DM structures during this period will encode those phase space information and be observed at present. Crucial condition λ_fs

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