Dark matter cooling during early matter-domination boosts sub-earth halos
arXiv:2408.08360 · doi:10.1088/1475-7516/2025/03/030
Abstract
The existence of an early matter-dominated epoch prior to the Big Bang Nucleosynthesis may lead to a scenario where the thermal dark matter cools faster than plasma before the radiation-dominated era begins. In the radiation-dominated epoch, dark matter free-streams after it decouples both chemically and kinetically from the plasma. In the presence of an early matter-dominated era, chemical decoupling of the dark matter may succeed by a partial kinetic decoupling before reheating ends, depending upon the contributions of different partial wave amplitudes in the elastic scattering rate of the dark matter. We show that the s-wave scattering is sufficient to partially decouple the dark matter from the plasma, if the entropy injection during the reheating era depends on the bath temperature, while p-wave scattering leads to full decoupling in such cosmological backdrop. The decoupling of dark matter before the end of reheating causes an additional amount of cooling, reducing its free-streaming horizon compared to the usual radiation-dominated cosmology. The enhanced matter perturbations for scales entering the horizon prior to the end of reheating, combined with the reduced free-steaming horizon, increase the number density of sub-earth mass halos. The resulting boost in the dark matter annihilation signatures could offer an intriguing probe to differentiate pre-BBN non-standard cosmological epochs. We show that the free-streaming horizon of the dark matter requires to be smaller than a cut-off to ensure a boost in the sub-earth halo populations. As case studies we present two examples: one for a scalar dark matter with -wave elastic scattering and the other one featuring a fermionic dark matter with -wave elastic scattering. We identify regions of parameter space in both models where the dark matter kinetically decouples during reheating, amplifying small-scale structure formation.
32 pages, 10 captioned figures, Comments are welcome. v2: references updated, matches JCAP version
References in corpus (41)
- A direct empirical proof of the existence of dark matter
- Ultralight scalars as cosmological dark matter
- Precise Relic WIMP Abundance and its Impact on Searches for Dark Matter Annihilation
- Reheating in Inflationary Cosmology: Theory and Applications
- A search for ultra-light axions using precision cosmological data
- Effects of cold dark matter decoupling and pair annihilation on cosmological perturbations
- Reheating and Post-inflationary Production of Dark Matter
- The 21cm angular-power spectrum from the dark ages
- Inflaton Oscillations and Post-Inflationary Reheating
- Gravitational Production of Dark Matter during Reheating
- Enhancement of the Dark Matter Abundance Before Reheating: Applications to Gravitino Dark Matter
- Pulsar Timing Probes of Primordial Black Holes and Subhalos
- Dynamics of oscillating scalar field in thermal environment
- How warm are non-thermal relics? Lyman- bounds on out-of-equilibrium dark matter
- Gravitational portals in the early Universe
- Non-thermal Histories and Implications for Structure Formation
- Dissipative Effects on Reheating after Inflation
- Gravitational reheating
- Probing Dark Matter Substructure with Pulsar Timing
- Ultra-cold WIMPs: relics of non-standard pre-BBN cosmologies
- Gravity as a Portal to Reheating, Leptogenesis and Dark Matter
- Scattering searches for dark matter in subhalos: neutron stars, cosmic rays, and old rocks
- WIMPs during Reheating
- From WIMPs to FIMPs with Low Reheating Temperatures
- Increasing Temperature toward the Completion of Reheating
- Breaking a dark degeneracy: The gamma-ray signature of early matter domination
- Dark Matter Microhalos From Simplified Models
- Kinetic decoupling of WIMPs: analytic expressions
- Energy Spectrum of Thermalizing High Energy Decay Products in the Early Universe
- Two phase reheating: CMB constraints on inflaton and dark matter phenomenology
- Measuring Inflaton Couplings via Primordial Gravitational Waves
- Confronting Dark Matter Freeze-In during Reheating with Constraints from Inflation
- Unitarity limits on thermal dark matter in (non-)standard cosmologies
- Cascades of high-energy SM particles in the primordial thermal plasma
- Primordial black holes and gravitational waves from dissipation during inflation
- Snowmass2021 Cosmic Frontier White Paper: Dark Matter Physics from Halo Measurements
- Dark Matter Microhalos in the Solar Neighborhood: Pulsar Timing Signatures of Early Matter Domination
- Dilaton dominance in the early Universe dilutes Dark Matter relic abundances
- Unitarity Bound on Dark Matter in Low-temperature Reheating Scenarios
- Frozen-in fermionic singlet dark matter in non-standard cosmology with a decaying fluid
- Inflationary Gravitational Waves as a probe of the unknown post-inflationary primordial Universe