Primordial Black Holes as All Dark Matter (1001.2308v2)

Abstract: We argue that a primordial black hole is a natural and unique candidate for all dark matter. We show that, in a smooth-hybrid new double inflation model, a right amount of the primordial black holes, with a sharply-defined mass, can be produced at the end of the smooth-hybrid regime, through preheating. We first consider masses < 10^-7M_sun which are allowed by all the previous constraints. We next discuss much heavier mass 10^5 M_sun hinted at by entropy, and galactic size evolution, arguments. Effects on the running of the scalar spectral index are computed.

• The paper demonstrates that a dual inflation model produces PBHs with sharply defined mass ranges capable of accounting for all dark matter.
• It identifies two specific mass ranges—below 10⁻⁷ and around 10⁵ solar masses—that align with cosmological observations.
• The study proposes testable correlations between PBH properties and cosmological parameters like the scalar spectral index and its running.

Primordial Black Holes as a Dark Matter Candidate

The paper "Primordial Black Holes as All Dark Matter," authored by Frampton et al., explores the intriguing hypothesis that primordial black holes (PBHs) could account for all dark matter (DM) in the universe. This supposition is investigated within the framework of a smooth-hybrid new double inflation model, resulting in specific PBH mass ranges consistent with contemporary cosmological constraints.

Summary of Key Proposals

The authors propose that PBHs are a natural and unique candidate for the entirety of dark matter, challenging the predominant WIMP-based models. Their paper focuses on two specific PBH mass ranges: masses less than $10^{-7}M_{\odot}$ and those significantly heavier, around $10^5M_{\odot}$. The model exploits a smooth-hybrid new double inflation mechanism, which enables the formation of PBHs with a sharply defined mass through the preheating process. This model also incorporates the computation of effects on the running of the scalar spectral index, a key parameter in determining the primordial power spectrum.

Numerical and Theoretical Findings

The paper demonstrates how PBHs of mass up to $10^5M_{\odot}$ could indeed comprise all DM, subject to observational constraints. Notably, the effective potential derived for smooth-hybrid inflation reveals that PBHs with masses from approximately $10^{-8}M_\odot$ to $10^5M_\odot$ can be produced. These findings are juxtaposed with data from the WMAP regarding curvature perturbations and the scalar spectral index.

The theoretical model predicts certain correlations between the PBH mass and cosmological observables, such as the spectral index $n_s$, and its running, which can be tested against future CMB observations. For instance, the predicted mass range relates to distinct but empirically testable relationships between the scalar spectral index and its running, potentially verifiable by the Planck satellite.

Implications

The implications of PBHs as a dark matter candidate are noteworthy. Unlike many proposed DM particles requiring modifications or extensions to the Standard Model, PBHs naturally fit within existing physics frameworks. Their gravitational interactions suffice to explain current observational data, negating the need for new particles or forces.

If PBHs account for all dark matter, they could influence various astrophysical phenomena, from microlensing events in galactic halos to the evolution of galaxy sizes, potentially reshaping our understanding of cosmic structure formation.

Future Research Directions

Further research is needed to substantiate the claims of this paper. Analyzing the gravitational effects of PBHs, such as through detailed microlensing observations or binary star analyses, might provide additional evidence or constraints on this hypothesis. Moreover, exploring the implications of PBH evaporation and accretion could yield more insights into the viability of PBHs as a complete explanation for dark matter.

In conclusion, the research by Frampton et al. proposes an innovative and theoretically sound argument for PBHs as a full substitute for dark matter. The model aligns with existing observational constraints and offers testable predictions for future astrophysical surveys, thereby providing a valuable alternative perspective within the continuous endeavor to unveil the enigma of dark matter.