Primordial Black Hole Hot Spots and Nucleosynthesis (2501.05531v1)

Abstract: Upon their evaporation via Hawking radiation, primordial black holes (PBHs) may deposit energy in the ambient plasma on scales smaller than the typical distance between two black holes, leading to the formation of hot spots around them. We investigate how the corresponding rise of the local temperature during the evaporation may act as a shield against the release of low-energy photons, affecting PBH's capacity to dissociate light nuclei after Big-Bang Nucleosynthesis through photo-dissociation. We study the different ways PBH hot spots affect the flux of low-energy photons expected from PBH evaporation, and we find that such effects can be particularly relevant to the physics of photo-dissociation during Big-Bang Nucleosynthesis for PBHs with masses between $10^{11}$g and $3\times 10^{12}$g. We emphasize that the magnitude of this effect is highly dependent on the specific shape of the temperature profile around PBHs and its time evolution. This underscores the necessity for a comprehensive study of PBH hot spots and their dynamics in the future.

• The paper demonstrates that localized hot spots around evaporating PBHs significantly alter photon behavior during nucleosynthesis.
• It quantifies how temperature variations reduce low-energy photon flux and shield light nuclei from photodissociation.
• The findings suggest that incorporating inhomogeneous thermal effects can relax existing constraints on PBH abundance in cosmological models.

Analysis of "Primordial Black Hole Hot Spots and Nucleosynthesis"

The paper "Primordial Black Hole Hot Spots and Nucleosynthesis" presents a nuanced paper of the influence of primordial black holes (PBHs) on nucleosynthesis in the early universe. The authors investigate the dynamic environment around evaporating PBHs and its potential impact on the photo-dissociation of light nuclei formed during Big Bang Nucleosynthesis (BBN). This work provides a novel perspective on the local thermal effects generated by PBH evaporation, which could challenge conventional assumptions of homogeneity during this epoch.

Context and Motivation

Primordial black holes are remnants from the early universe, theorized to form from over-dense regions shortly after the Big Bang. Although smaller PBHs (less than about $10^{15}$ grams) would have evaporated due to Hawking radiation by now, their effect on the early universe remains an important research topic. One of the key impacts is their contribution to the process of nucleosynthesis, particularly through the injection of energy and particles, which can alter the relative abundances of light elements like helium and deuterium.

The authors focus on PBHs with masses between $10^{11}$ and $3 \times 10^{12}$ grams. During their evaporation phase, these PBHs release energy that can form localized hot spots with distinct temperature profiles. The potential for these hot spots to act as shields against the escape of low-energy photons, which are pivotal in the photo-dissociation of nuclei, adds complexity to the understanding of how PBHs might influence BBN.

Key Findings

1. Local versus Global Temperature Effects: The paper critically analyzes the assumption of spatial homogeneity in the impact of PBH radiation. The authors demonstrate that the temperature profile surrounding PBHs can significantly change the behavior of reprocessed photons, thus affecting the photodissociation rates of light nuclei.
2. Influence of Hot Spot Dynamics: The formation of hot spots results in a temperature increase that can alter the mean free path of photons. Consequently, photon shielding occurs, reducing the PBH's influence on nucleosynthesis through direct photodissociation. The paper provides a quantifiable measure of how these local temperature variations reduce the low-energy photon flux, particularly for PBHs with the specified mass range.
3. Impact on Constraints of PBH Abundance: By modifying the universal photon spectrum, the authors suggest that the presence of hot spots can relax the current constraints on the abundance of PBHs. This implies that previous models may have overestimated this abundance due to a lack of consideration for heterogeneous thermal conditions.

Theoretical and Practical Implications

This research prompts a reevaluation of PBH-induced cosmological phenomena, suggesting that inhomogeneities and local thermal dynamics might play more significant roles than previously acknowledged. The shielding effect and local reheating phenomena discussed could lead to adjusted parameters for PBH impacts on BBN-derived constraints, thereby aiding in the refinement of cosmological models.

On a practical level, this paper suggests areas for future research, such as improved modeling of the thermal environment around PBHs and the continuation of calculations beyond the homogeneous assumptions often used in BBN analyses. Additionally, integrating considerations for interactions below certain particle masses, such as electrons, remains a fruitful area for further exploration.

Future Directions in Research

Further studies should seek to extend these findings by exploring different scenarios of particle interactions and thermal profile evolutions in varying cosmological settings. The authors also imply a need for more sophisticated models to simulate high-energy particle showers within the hot spot environment accurately. These simulations can offer deeper insights into the complex dynamics around PBHs and provide more comprehensive constraints that integrate the probable effects of black hole microphysics.

In conclusion, this paper presents a compelling case for localized modeling of PBH impacts on nucleosynthesis. By challenging the assumptions of isotropy and homogeneity, the authors open new avenues for understanding the early universe's intricacies, with implications that could refine the constraints on PBH populations and their roles in cosmology.