Breakdown of Hawking Evaporation opens new Mass Window for Primordial Black Holes as Dark Matter Candidate (2402.17823v2)

Abstract: The energy injection through Hawking evaporation has been used to put strong constraints on primordial black holes as a dark matter candidate at masses below $10^{17}\,\rm{g}$. However, Hawking's semiclassical approximation breaks down at latest after half-decay. Beyond this point, the evaporation could be significantly suppressed, as was shown in recent work. In this study, we review existing cosmological and astrophysical bounds on primordial black holes, taking this effect into account. We show that the constraints disappear completely for a reasonable range of parameters, which opens a new window below $10^{10}\,\rm{g}$ for light primordial black holes as a dark matter candidate.

• The paper demonstrates that incorporating quantum memory effects significantly reduces the evaporation rate, establishing a viable sub-10^10 g mass window for PBHs.
• It employs a semi-analytical model that integrates constraints from gamma-ray, CMB, and BBN observations to challenge traditional evaporation limits.
• The study’s findings encourage further investigations into quantum gravitational effects and their implications for primordial black holes as dark matter candidates.

Analysis of Constraints on Primordial Black Holes as Dark Matter Candidates

The paper by Thoss et al. (2024) explores a compelling avenue in the domain of cosmology and astrophysics, focusing on the hypothesis of primordial black holes (PBHs) as viable candidates for constituting dark matter. The investigation is directed towards revisiting the established constraints on PBHs when considering a breakdown of Hawking’s semiclassical (SC) approximation of black hole evaporation. This recalibration of constraints is facilitated by incorporating the effects of a significant reduction in the evaporation rate due to the "memory burden" effect, a concept introduced by Dvali (2018).

The paper scrutinizes the implications of this breakdown on the evaporative process, especially highlighting a new parameter mass window for PBHs as dark matter candidates. It specifically indicates that by considering the quantum backreaction—the memory burden—the constraints on PBHs can be reevaluated, potentially opening a mass window below 10^10 g. This proposed mass window challenges traditional views, which are restricted by constraints from various observations including gamma-ray background and cosmic microwave background (CMB) studies.

Methodological Framework

The authors employ a modified model of black hole evaporation that diverges from the SC approach traditionally informed by Hawking's calculations. The memory burden effect suggests a suppression in the evaporation rate, parameterized by an exponent $k$, which depends on the black hole's entropy. This has profound implications for the paper of PBHs, as it implies that black holes might not fully evaporate but instead stabilize with lower mass remnants. The paper elucidates this phenomenon using a semi-analytical approach and conducts detailed computational modeling, integrating constraints from cosmological and astrophysical observations.

The central focus of the paper is to assess the constraints on PBHs that stem from varying observational data, notably gamma-ray emissions both galactic and extragalactic, as well as CMB anisotropies. This is complemented by a rigorous exploration of the early universe's light element abundances produced during big bang nucleosynthesis (BBN).

Results

The results of the paper challenge existing paradigms by illustrating that for $k > 1.0$, a new mass window arises where PBHs could satisfactorily account for all dark matter. This range extends up to approximately 10^10 g, with the lifetime of such PBHs being substantially increased beyond the conventional SC expectations. The analysis delineates the conditions under which PBHs could have survived to the present epoch, thereby making them a significant component of dark matter.

A noteworthy outcome is the identification of conditions under which the new constraints are relaxed compared to the steep SC limitations, particularly in the context of BBN and CMB observations where constraints are considerably weaker. It also demonstrates that for masses exceeding about 10^13 g, no significant alteration in constraints occurs since the SC evaporation phase remains largely insightful after recombination.

Implications and Future Directions

This paper embarks on a crucial re-examination journey, paving the way for introducing PBHs as potential dark matter constituents under revised theoretical models incorporating quantum gravitational effects. The new mass window for PBHs compels a reevaluation of their roles in cosmic structure formation and evolution, potentially altering our understanding of cosmological mass distribution.

From a theoretical standpoint, this paper intensifies the necessity for a deeper comprehension of black hole quantum mechanics, especially around the final stages of evaporation. A resolution of the uncertainties around the emission spectra and the thermodynamic attributes of black holes in the post-SC regime is essential for strengthening these revised constraints.

Moreover, the paper accentuates the importance of future observational advancements. The potential detection or non-detection of PBHs within this newly proposed mass range could provide critical empirical data for direct validation of theoretical predictions, thereby enhancing our understanding of both PBHs and dark matter.

In conclusion, Thoss et al.'s (2024) paper offers a significant amendment to the understanding of primordial black holes. While acknowledging the limitations of current models and constraints, it presents a refreshed perspective that could stimulate further research in the fields of cosmology and quantum gravitational dynamics. The implications of these findings may extend into broader domains, including the formation of cosmic structures and the evolution of the early universe, holding potential to substantially impact theories surrounding dark matter.