Black Hole Metamorphosis and Stabilization by Memory Burden (2006.00011v3)

Abstract: Systems of enhanced memory capacity are subjected to a universal effect of memory burden, which suppresses their decay. In this paper, we study a prototype model to show that memory burden can be overcome by rewriting stored quantum information from one set of degrees of freedom to another one. However, due to a suppressed rate of rewriting, the evolution becomes extremely slow compared to the initial stage. Applied to black holes, this predicts a metamorphosis, including a drastic deviation from Hawking evaporation, at the latest after losing half of the mass. This raises a tantalizing question about the fate of a black hole. As two likely options, it can either become extremely long lived or decay via a new classical instability into gravitational lumps. The first option would open up a new window for small primordial black holes as viable dark matter candidates.

• The paper introduces the concept of memory burden, which delays black hole evolution by rewriting quantum information across different degrees of freedom.
• It employs a microscopic model based on the quantum N-portrait to analyze graviton interactions and the subsequent slowdown in evaporation.
• The findings suggest that stabilized primordial black holes may persist as viable dark matter candidates despite classical instability conditions.

Overview of "Black Hole Metamorphosis and Stabilization by Memory Burden"

The paper "Black Hole Metamorphosis and Stabilization by Memory Burden," authored by Gia Dvali and colleagues, introduces a framework for understanding the stabilization properties of systems with enhanced memory capacity, especially focusing on black holes. The notion of memory burden emerges as a crucial concept in describing how systems with high-memory capacity suppress decay and interact with their stored information.

Theoretical Framework and Model

The authors explore a prototype model to illustrate the effect of memory burden on systems of enhanced memory capacity. The central hypothesis is that rewriting quantum information across different degrees of freedom can counteract memory burden. However, this rewriting process is significantly slow, which delays the evolution of the system considerably. Applied within the context of black holes, this framework suggests a paradigm shift from the traditional view of Hawking evaporation.

The paper outlines two potential outcomes for black holes undergoing metamorphosis: either they become extremely long-lived or disintegrate due to a new classical instability, potentially transforming into gravitational lumps. The first outcome offers a perspective that positions small primordial black holes as plausible dark matter candidates.

Numerical and Theoretical Analysis

The examination involves the detailed paper of a microscopic theory describing black holes as bound states of soft gravitons—referred to as the quantum N-portrait. Here, the critical number $N_c$ of gravitons and their weak interactions play pivotal roles. This criticality allows for computations and predictions about the evolution and storage capacity using effective field theories, augmented by a $1/N$ expansion approach.

Key numerical findings suggest memory burden effects intensify as black holes lose mass, specifically manifesting notably after they lose around half their mass. The paper employs assisted gapless modes in the prototype model to replicate high capacity of memory storage, leading to considerations of the implications for black hole thermodynamics and evaporative behaviors.

Implications for Black Holes and Cosmology

The paper infers potential scenarios for the evolution of black holes after substantial mass loss due to the memory burden effect. This potentially alters our understanding of black holes as evaporation proceeds beyond the semi-classical prediction landscape, typically constrained by Hawking's computations.

Black hole stabilization by memory burden also posits implications for cosmic observations, particularly regarding primordial black holes as dark matter candidates. The paper discusses how these findings could reconcile with constraints from gamma-ray backgrounds and nucleosynthesis, proposing a fascinating narrative where small primordial black holes remain viable dark matter despite evaporation challenges.

Conclusion and Future Directions

In summary, the research by Dvali et al. proposes that the stabilization—through memory burden—of systems with high memory capacity, such as black holes, presents substantial deviations from the conventional understanding of their lifecycle. The notion of sustainable black holes or their transition into new forms has implications not only for black hole physics but also for broader cosmological studies.

Speculation on the pathway beyond the metamorphosis stage invites further exploration into the potential classical instabilities and new observational strategies for detecting primordial black holes. This avenue is likely to invigorate future theoretical and observational research agendas, targeting new insights into the lifecycle and fundamental nature of black holes in our universe.