New Mass Window for Primordial Black Holes as Dark Matter from Memory Burden Effect (2402.14069v1)

Abstract: The mass ranges allowed for Primordial Black Holes (PBHs) to constitute all of Dark Matter (DM) are broadly constrained. However, these constraints rely on the standard semiclassical approximation which assumes that the evaporation process is self-similar. Quantum effects such as memory burden take the evaporation process out of the semiclassical regime latest by half-decay time. What happens beyond this time is currently not known. However, theoretical evidence based on prototype models indicates that the evaporation slows down thereby extending the lifetime of a black hole. This modifies the mass ranges constrained, in particular, by BBN and CMB spectral distortions. We show that previous constraints are largely relaxed when the PBH lifetime is extended, making it possible for PBHs to constitute all of DM in previously excluded mass ranges. In particular, this is the case for PBHs lighter than $10^9$g which enter the memory burden stage before BBN and are still present today as DM.

• The paper demonstrates that the memory burden effect slows traditional black hole evaporation, extending PBH lifetimes beyond semiclassical predictions.
• The authors use a theoretical framework with black holes as coherent graviton states to challenge established evaporation models.
• The paper identifies a new parameter space where PBHs as light as 10^6 g could survive BBN and contribute significantly to dark matter.

Overview of "New Mass Window for Primordial Black Holes as Dark Matter from Memory Burden Effect"

This paper explores the possibility that Primordial Black Holes (PBHs) could account for a significant fraction of dark matter, focusing specifically on the implications of a "memory burden effect" that modifies the conventional understanding of black hole evaporation. Authored by Ana Alexandre, Gia Dvali, and Emmanouil Koutsangelas, the work seeks to explore new mass ranges for PBHs, challenging previously accepted constraints by introducing concepts beyond the semiclassical approximations traditionally used in these calculations.

Key Arguments and Methodology

The fundamental premise of this work is that the standard semiclassical approximation, which assumes a self-similar evaporation process for black holes, is no longer valid beyond the half-decay time of the black hole's lifecycle. Instead, quantum effects, notably the "memory burden effect," are suggested to slow down the evaporation process, thus extending the lifetime of black holes beyond what traditional models predict.

The authors provide theoretical evidence, positing that a microscopic view of black holes as coherent states of gravitons aligns with a deviation from the semiclassical framework. This departure suggests that black holes enter a non-semiclassical regime after they have emitted approximately half of their initial mass. Consequently, this memory burden dramatically alters the mass ranges that have been deemed inconsistent with observations such as Big Bang Nucleosynthesis (BBN) and Cosmic Microwave Background (CMB) spectral distortions.

Numerical Results and Theoretical Implications

By introducing a new approach to the dynamics of black holes, the paper recalculates the evaporation timelines. Specifically, it argues that PBHs lighter than $10^9$g could survive the BBN period and persist to the present epoch while contributing to dark matter. The original Hawking evaporation time is contrasted with a new model that incorporates additional powers of the entropy term, ostensibly extending the lifetimes significantly and relaxing previous constraints on the mass.

The implications are substantial: PBHs across a wider mass range, specifically as low as $10^6$g, become viable candidates for composing dark matter. Through a detailed scrutiny of the emitted energy density and the impact on BBN and CMB epochs, a novel parameter space is proposed. This parameter space highlights mass regions where PBHs were previously excluded but now demand reconsideration under this new framework.

Practical Implications and Future Directions

The practical implication of this research is a widened potential for PBHs to constitute a larger portion of dark matter than traditionally assumed. This is contingent on the corroboration of the memory burden effect and its impact on black hole physics.

Future research could entail exploring further quantum mechanical implications on black hole dynamics and pursuing observational strategies that can validate these theoretical predictions. Additionally, understanding the boundaries and exact nature of the new mass window will be critical, particularly as high-precision cosmological data continue to refine our understanding of the early universe.

Conclusion

This paper makes a compelling case for re-examining the role of PBHs in dark matter scenarios through a quantum-augmented lens. By challenging the standard paradigms and employing innovative concepts like the memory burden effect, it opens a conceptual arena that could substantially impact theoretical physics and cosmology. Further empirical exploration and theoretical refinement will be essential to ascertain the feasibility and implications of these proposed models.