De Sitter Decay Produces Planck-Size Black Holes, Potentially Explaining Dark Matter

The enduring mystery of dark matter may find an unexpected solution in the very fabric of spacetime, according to new research. Bernard Carr from Queen Mary University of London, Piero Nicolini from the University of Trieste and Istituto Nazionale di Fisica Nucleare, and Athanasios G. Tzikas from Johann Wolfgang Goethe-Universität Frankfurt am Main and University of Bergamo, demonstrate that the decay of de Sitter space, a theoretical expansion of the universe, can produce stable, Planck-size black holes. Contrary to previous assumptions, this process continues even after the initial period of cosmic inflation and occurs at a rate sufficient to account for the observed abundance of dark matter within our galactic neighbourhood. The team’s calculations suggest these primordial black holes, remnants of the universe’s earliest moments, offer a compelling explanation for this elusive substance, potentially resolving a long-standing problem in cosmology and particle physics

Black Hole Formation After Inflation Matters

This research investigates the possibility that primordial black holes, formed after the inflationary period following the Big Bang, could account for the observed dark matter in the universe. It challenges the conventional understanding that black hole production during this epoch is insignificant, proposing that a specific distribution of mass could dramatically increase the rate of black hole formation and offer a novel perspective on the nature of dark matter and its connection to the expanding universe. The core argument centres on the decay of de Sitter space, a theoretical framework describing a universe with a positive cosmological constant, like our own, and its implications for spontaneous black hole nucleation. Previous calculations suggested this process was too slow to produce substantial dark matter, but this paper demonstrates that, by considering a more nuanced cumulative mass distribution, the rate of black hole production can become significant enough to potentially explain the missing mass observed by astronomers, offering a compelling alternative to Weakly Interacting Massive Particles (WIMPs) and axions, the leading candidates in particle physics models.

This altered perspective alters the structure of the event horizon, enabling black hole formation even with a relatively small cosmological constant following inflation. The cosmological constant, often denoted by Λ (Lambda), represents the energy density of space itself and drives the accelerated expansion of the universe. The research builds upon the established framework of eternal chaotic inflation, which posits that our universe is just one bubble within a larger multiverse constantly undergoing expansion, with different regions experiencing varying rates of inflation and different values of the cosmological constant. Utilizing established mathematical tools, such as the Bousso-Hawking formalism, a method for calculating the rate of particle creation in de Sitter space, the authors quantify the number of black holes produced within the observable universe, accounting for its ongoing expansion and the associated dilution of dark matter density. The formalism relies on concepts from quantum field theory in curved spacetime, where the gravitational field influences the creation and annihilation of particles, and the results demonstrate that the decay rate of the cosmological constant can be non-negligible after inflation when this cumulative mass distribution is considered, leading to a substantial increase in black hole nucleation.

The calculations suggest that approximately 10⁶⁰ black holes could be produced, a number sufficient to potentially account for the observed dark matter. These primordial black holes, unlike those formed from stellar collapse, are thought to have a wide range of masses, potentially spanning from asteroid-mass objects to those comparable to stars. Importantly, the universe remains quantum mechanically stable throughout this process, as the rate of black hole formation is slow enough to not disrupt the overall expansion, with the probability of black hole production within each expanding bubble of space estimated to be approximately 10^-12, which can accumulate over cosmological timescales to explain the observed dark matter density. This research offers a compelling alternative explanation for the nature of dark matter, proposing that it consists of primordial black holes formed through the decay of the cosmological constant, and it avoids the need for new, undiscovered particles beyond the Standard Model of particle physics. The mass of these black holes is crucial; if they fall within a specific range, they could also contribute to the observed gravitational wave background, offering a potential avenue for observational verification.

This work opens up new avenues for future research, including exploring the effects of different mass distributions and searching for observational signatures of these primordial black holes. Future investigations could focus on refining the calculations by incorporating more complex cosmological models and exploring the impact of different inflationary scenarios. Observational searches could involve looking for gravitational lensing effects caused by these black holes, or searching for their signatures in the cosmic microwave background. In simpler terms, imagine the universe expanding rapidly after the Big Bang. Traditionally, scientists believed that any black holes forming during this expansion would be too spread out to have a significant impact. This paper proposes that if mass is distributed in a slightly different way than previously assumed, enough black holes could form to account for the mysterious dark matter we observe today, representing a new way of thinking about how dark matter might have originated and suggesting a stronger connection between the expansion of the universe and the formation of black holes. The implications extend beyond dark matter, potentially offering insights into the very early universe and the nature of the cosmological constant itself.