Memory-burdened Primordial Black Holes Constrained Via Graviton-Photon Conversion and Mergers Today

Primordial black holes remain compelling candidates for dark matter, yet their existence faces stringent constraints from observations of their evaporation products. Po-Yan Tseng and Yu-Min Yeh, from National Tsing Hua University, investigate how a phenomenon called the ‘memory-burden effect’ influences the survival of these black holes and opens up new possibilities for their detection. The researchers propose two innovative methods to probe black holes evaporating at higher rates, focusing on both the conversion of emitted gravitons into detectable photons and the observation of mergers that create younger, rapidly evaporating black holes. By modelling the expected gamma-ray signals from these processes and comparing them with current observational limits, the team establishes new constraints on the abundance of primordial black holes, excluding certain mass ranges and significantly refining the search for this elusive form of dark matter.

Hawking Radiation and Black Hole Memory

Scientists are investigating primordial black holes (PBHs) as potential dark matter candidates, focusing on how quantum effects modify their evaporation and extend their lifetimes. The research addresses a key challenge, the rapid evaporation of low-mass PBHs, by incorporating the memory burden effect, a phenomenon where the black hole’s internal quantum state resists decay and slows evaporation. This effect becomes significant as a PBH loses mass, altering the evaporation process and opening a new window for PBHs to constitute dark matter. Essentially, the black hole doesn’t fully evaporate, leaving a remnant that can persist longer.

Researchers are exploring methods to detect or constrain these memory-burdened PBHs, utilizing sophisticated codes to calculate the spectra of particles emitted during evaporation and predicting observable signals. A primary search target is high-energy gamma rays, predicted to be emitted as burdened PBHs evaporate, with observations from instruments like LHAASO proving relevant. Furthermore, the evaporation process can produce gravitational waves, and mergers between burdened PBHs might create detectable signals for observatories like LIGO and Virgo. Scientists are even investigating the possibility of detecting gravitational waves alongside electromagnetic signals, such as gamma rays, from evaporating PBHs.

The memory burden effect opens up new mass ranges for PBHs to be viable dark matter candidates. Recent work attempts to constrain burdened PBHs using observations from Big Bang Nucleosynthesis and the Planck satellite. Researchers are also looking for correlations between different signals, such as gravitational waves and gamma rays, to improve detection prospects. This research explores the possibility that primordial black holes, stabilized by the memory burden effect, could be a significant component of dark matter.

Quantum Memory Extends Primordial Black Hole Lifetimes

Scientists investigated how quantum effects modify the evaporation of primordial black holes (PBHs) and extend their lifetimes, potentially resolving constraints imposed by Hawking evaporation. The research focuses on the memory burden effect, where the black hole’s internal quantum state resists decay and slows evaporation. This effect becomes significant when a PBH loses approximately half its initial mass, transitioning it into a phase where evaporation is suppressed. Researchers modeled this suppression, allowing them to explore a wider range of PBH masses as viable dark matter candidates. To probe PBHs in their early, rapidly evaporating phase, the study pioneered two distinct scenarios.

The first involves gravitons, hypothetical particles mediating gravity, emitted from PBHs before the universe became transparent to light. These gravitons convert into photons, particles of light, via the Gertsenshtein effect when interacting with magnetic fields present in cosmological filaments, vast structures of matter spanning the universe. The team calculated the probability of this conversion, leveraging the properties of cosmological filaments to enhance the detectability of the signal. The second scenario focuses on PBH mergers, which recreate young black holes with unsuppressed evaporation rates.

Scientists then calculated the expected photon flux from both scenarios, considering the sensitivities of current and future gamma-ray telescopes. By comparing these predicted fluxes with observational upper limits, the team established constraints on the abundance of PBHs, ultimately restricting the viable mass range for PBH dark matter. The research utilized the BlackHawk v2. 3 package to model the memory burden effect and accurately simulate the complex interplay between quantum mechanics, gravity, and particle physics.

Stabilized Primordial Black Holes Resist Evaporation

Scientists have demonstrated that the memory-burden effect stabilizes evaporating Primordial Black Holes (PBHs), extending their lifespan and suppressing the rate of their evaporation. This stabilization occurs because the quantum state of the black hole resists complete decay, slowing mass loss as a significant fraction of the initial mass has evaporated. Researchers calculated that when a PBH loses half its initial mass, the evaporation rate is governed by an entropy factor. The team investigated two scenarios to probe PBHs in their earlier, rapidly evaporating phase. The first considers gravitons emitted from PBHs, which propagate through the universe and convert into photons via the Gertsenshtein effect in the presence of magnetic fields within cosmological filaments.

The second scenario focuses on PBH mergers today, creating younger black holes with unsuppressed evaporation rates. By calculating the expected extragalactic spectrum from PBH emission in both scenarios, scientists established upper limits on the fractional abundance of PBHs. Measurements reveal that the graviton-conversion scenario excludes a specific mass range, while the merging scenario, independent of this parameter, restricts PBH Dark Matter to lighter masses. Calculations show that for a PBH with an initial mass of 10 8 grams, the inclusion of the memory-burden effect significantly extends the PBH lifetime beyond the age of the universe. The team observed a double-peak structure in the graviton spectrum, with peaks originating from different phases of evaporation. This work establishes constraints on the fractional abundance of PBHs, demonstrating that the memory-burden effect and the Gertsenshtein effect provide powerful tools for probing the properties and abundance of primordial black holes.

Memory Burden Extends Primordial Black Hole Lifetimes

This research investigates the potential of primordial black holes as a component of dark matter, focusing on how the ‘memory burden’ effect alters their evaporation rate and extends the range of viable masses. Scientists have demonstrated that this effect, which arises from the backreaction of emitted particles on the black hole’s quantum state, suppresses evaporation and allows lighter black holes to persist for longer. This work opens a new mass window for primordial black holes to constitute dark matter. To probe these black holes, the team explored two scenarios for detecting signals from their evaporation.

The first involves gravitons, emitted during the black hole’s initial phase, converting into photons via the Gertsenshtein effect when interacting with magnetic fields in cosmological filaments. The second scenario considers mergers of primordial black holes, which recreate young black holes with unsuppressed evaporation rates. By modelling the expected gamma-ray spectrum from these emissions and comparing it with observational sensitivities, researchers established upper limits on the fractional abundance of primordial black holes. The authors acknowledge that their analysis relies on certain assumptions regarding the strength and distribution of magnetic fields in cosmological filaments, which introduces some uncertainty into the results.