A new preprint on arXiv (2604.00090) explores how primordial black holes (PBHs) influenced by a 'memory burden' effect can produce non-cold dark matter (NCDM) particles. This theoretical work, which remains unpublished in a peer-reviewed journal, uses numerical simulations to show that PBH evaporation creates two distinct dark matter populations with different velocity dispersions. The study employs the BlackHawk code to model the evaporation spectra across a semi-classical phase followed by a memory-burden-dominated phase, then feeds these results into the CLASS cosmological Boltzmann code to compute the matter power spectrum. No observational sample is involved; instead, researchers reinterpret existing Lyman-α forest data, which probes small-scale structure through absorption lines in quasar spectra from the early universe.

The memory burden mechanism, drawn from quantum gravity considerations, slows the final stages of black hole evaporation as the system retains information, altering the energy and momentum distribution of emitted particles compared to pure Hawking radiation. This leads to NCDM that is warmer than standard cold dark matter (CDM) but not as extreme as typical warm dark matter (WDM) models. The paper demonstrates that even a subdominant fraction of such NCDM can suppress small-scale overdensities enough to be constrained by Lyman-α observations, while full NCDM as all dark matter remains viable only if PBHs never dominated the early universe's energy budget.

This work goes beyond standard PBH evaporation studies by incorporating the memory burden, an effect proposed in papers such as arXiv:2205.01624 (Dvali et al. on black hole memory burden) that previous NCDM-from-PBH analyses largely overlooked. It synthesizes these ideas with Lyman-α constraints from Iršič et al. (arXiv:1911.11716), which set tight bounds on thermal WDM particle masses around 5-6 keV using high-redshift forest data. Traditional coverage of CDM tensions often focuses on simulations like those addressing the core-cusp and missing-satellites problems but misses how a natural particle production mechanism from PBHs could simultaneously address multiple small-scale discrepancies without invoking entirely new fields.

Genuine analysis: This model offers a compelling alternative to purely particle-physics solutions like ultra-light axions or self-interacting dark matter. By linking PBH formation in the early universe to late-time structure, it connects inflation-era physics with galaxy-scale observations. However, limitations are significant: the memory burden parameter remains theoretically motivated but untested, results depend sensitively on assumed PBH initial mass function and abundance, and Lyman-α constraints carry systematic uncertainties from modeling the intergalactic medium. The absence of PBH domination is required for the all-NCDM case, narrowing the window. Still, this approach elegantly ties together gravitational, quantum, and cosmological threads that standard CDM treats separately, potentially easing σ8 and small-scale structure tensions without new fundamental particles.