Primordial Black Holes in Extra Dimensions and High-Energy Neutrino Signals.

Research indicates that established mechanisms for primordial black hole formation, within the Dark Dimension Scenario—a theoretical framework informed by string theory—predict the creation of five-dimensional primordial black holes. Cosmic strings may produce black holes with lifespans comparable to the universe’s age, potentially linking to high-energy neutrino detections like those from KM3NeT.

The enduring mystery of dark matter receives renewed attention in recent research exploring the potential role of primordial black holes, hypothesised to have formed in the very early universe. These black holes, unlike those formed from stellar collapse, could account for a significant portion of the missing mass and offer a compelling explanation for gravitational anomalies. A collaborative investigation, led by Luis A. Anchordoqui from Lehman College, City University of New York, alongside Alek Bedroya of the Princeton Gravity Initiative, Princeton University, and Dieter Lüst from the Max–Planck–Institut für Physik and Ludwig-Maximilians-Universität München, proposes a novel perspective on their formation. Their work, entitled ‘Primordial Black Holes are 5D’, revisits established mechanisms – inflation, phase transitions, and cosmic strings – within the framework of the ‘Dark Dimension Scenario’, a theoretical construct rooted in ‘Swampland’ principles, and demonstrates that these processes naturally lead to the creation of five-dimensional primordial black holes. The research further suggests a potential link between these high-dimensional black holes and the recent detection of a high-energy neutrino by the KM3NeT detector, a correlation that could offer a new avenue for observational verification.

Primordial black holes (PBHs) increasingly feature as viable candidates for comprising dark matter, particularly within the theoretical landscape of the Dark Dimension Scenario. This scenario, built upon principles derived from string theory known as Swampland constraints, posits the existence of extra spatial dimensions. Recent research re-examines established mechanisms for PBH production – namely, inflation, phase transitions, and cosmic strings – and demonstrates that, given current observational limits, these processes predominantly generate five-dimensional PBHs. Inflation refers to a period of rapid expansion in the very early universe, phase transitions describe changes in the state of matter as the universe cooled, and cosmic strings are hypothetical one-dimensional topological defects.

Notably, PBHs originating from cosmic strings exhibit potentially extended lifespans, comparable to the current age of the universe. This longevity arises from the specific properties of these higher-dimensional objects and their decay pathways. The study establishes a direct correlation between the predicted characteristics of these PBHs and recent astrophysical observations, specifically the detection of an ultra-high-energy neutrino by the KM3NeT collaboration. Neutrinos are fundamental particles with very small mass, and KM3NeT is a large neutrino telescope located in the Mediterranean Sea.

The research integrates concepts from particle physics, including axion models and the Peccei-Quinn mechanism, to explore potential connections between dark matter candidates and the properties of PBHs within these extra-dimensional frameworks. Axions are hypothetical elementary particles proposed as a component of dark matter, and the Peccei-Quinn mechanism is a theoretical solution to a problem in quantum chromodynamics. Researchers investigate how these solutions impact PBH formation and detectability, and consider the implications of Planck-scale corrections to axion models, potentially influencing their stability and contribution to the dark matter halo. The Planck scale represents the energy level at which quantum effects of gravity become significant.

The study reveals a potential connection to the recent detection of a high-energy cosmic neutrino by the KM3NeT collaboration, investigating how the detected neutrino originates from the decay or interaction of five-dimensional PBHs formed in the early universe. Scientists propose future observations, including enhanced neutrino detection and searches for correlated signals from other cosmic ray observatories, to confirm or refute the connection between PBHs and the observed neutrino flux. This work paves the way for a deeper understanding of the universe’s fundamental constituents and the processes that shaped its evolution, and encourages further investigation into the interplay between dark matter, extra dimensions, and high-energy cosmic rays.