Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and the seeds of Galaxies (1501.07565v1)

Abstract: In this paper we present a new scenario where massive Primordial Black Holes (PBH) are produced from the collapse of large curvature perturbations generated during a mild waterfall phase of hybrid inflation. We determine the values of the inflaton potential parameters leading to a PBH mass spectrum peaking on planetary-like masses at matter-radiation equality and producing abundances comparable to those of Dark Matter today, while the matter power spectrum on scales probed by CMB anisotropies agrees with Planck data. These PBH could have acquired large stellar masses today, via merging, and the model passes both the constraints from CMB distortions and micro-lensing. This scenario is supported by Chandra observations of numerous BH candidates in the central region of Andromeda. Moreover, the tail of the PBH mass distribution could be responsible for the seeds of supermassive black holes at the center of galaxies, as well as for ultra-luminous X-rays sources. We find that our effective hybrid potential can originate e.g. from D-term inflation with a Fayet-Iliopoulos term of the order of the Planck scale but sub-planckian values of the inflaton field. Finally, we discuss the implications of quantum diffusion at the instability point of the potential, able to generate a swiss-cheese like structure of the Universe, eventually leading to apparent accelerated cosmic expansion.

• The paper demonstrates that large curvature perturbations during a mild waterfall phase in hybrid inflation can trigger the formation of massive primordial black holes.
• The study uses detailed numerical modeling to estimate a PBH mass spectrum that aligns with dark matter observations and explains ultra-luminous X-ray sources.
• The research navigates CMB and microlensing constraints while proposing that these PBHs could merge to seed supermassive black holes and drive galaxy formation.

Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and the Seeds of Galaxies

The paper "Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and the Seeds of Galaxies" explores a provocative scenario where massive primordial black holes (PBH), arising from hybrid inflation, form a significant component, if not the entirety, of dark matter. The research investigates a mild waterfall phase during hybrid inflation, postulating that large curvature perturbations in this phase could lead to PBHs with planetary masses, possibly forming the seeds for galaxies or ultra-luminous X-ray sources.

Key Findings and Theoretical Implications

The authors employ an effective hybrid inflation potential to show that large curvature perturbations can be achieved under specific parameters. Such perturbations exceed the critical threshold necessary for gravitational collapse, resulting in PBH formation. The paper presents a model wherein:

• PBHs could emerge with planetary-like masses during matter-radiation equality and evolve into larger stellar masses through merging.
• The scenario successfully navigates constraints from CMB distortions and microlensing, suggesting compatibility with observational data.

This model sees support from astrophysical observations, such as those by the Chandra X-ray Observatory, which have identified numerous black hole candidates in Andromeda's central region. The observations could align with the expected distribution of black holes derived from this hybrid inflation model.

Numerical and Analytical Approaches

Through detailed numerical calculations, the paper estimates the mass spectrum of PBHs, arguing for their abundance to potentially align with dark matter observations. It suggests that these PBHs could have merged after formation, accounting for their absence in current microlensing surveys. Additionally, merging could help these PBHs account for phenomena such as supermassive black holes at galactic centers and ultra-luminous X-ray sources.

Constraints and Speculations

The research also explores the embedding of this effective potential within realistic high-energy physics frameworks. Specifically, D-term inflation models offer a plausible context when incorporating Planck-like values for the Fayet-Iliopoulos term. A notable discussion point from the paper is the hypothesis that PBHs can serve as seeds for supermassive black holes observed at high redshifts. This connects the model’s predictions with existing theoretical narratives on galaxy formation.

Future Prospects

Considering the theoretical and practical implications, several frontiers remain open for exploration:

• More detailed studies are needed to understand the dynamics of PBH growth and clustering.
• Future CMB observation missions and gravitational wave detections could provide pivotal tests for this model's viability.
• The possibility that large scale inhomogeneities might influence cosmic acceleration ares a topic warranting further scrutiny given the proposed quantum diffusion mechanisms in this model.

This paper contributes to the broader understanding of how primordial black holes, arising from inflationary dynamics, might serve as dark matter candidates and progenitors of cosmic structures. Exploring these avenues may yield significant insights into the intricate fabric of the Universe.