Exploring Primordial Black Holes from the Multiverse with Optical Telescopes

TL;DR

It is demonstrated with numerical studies that future observations of HSC, as well as other optical surveys, will be able to provide a definitive test for this generic PBH formation mechanism if it is the dominant source of dark matter.

Abstract

Primordial black holes (PBHs) are a viable candidate for dark matter if the PBH masses are in the currently unconstrained "sublunar" mass range. We revisit the possibility that PBHs were produced by nucleation of false vacuum bubbles during inflation. We show that this scenario can produce a population of PBHs that simultaneously accounts for all dark matter, explains the candidate event in Subaru Hyper Suprime-Cam (HSC) data, and contains both heavy black holes as observed by LIGO and very heavy seeds of supermassive black holes. We demonstrate with numerical studies that future observations of HSC, as well as other optical surveys, such as LSST, will be able to provide a definitive test for this generic PBH formation mechanism if it is the dominant source of dark matter.

Figures (3)

• Figure 1: Illustration of tilted "Mexican hat" potential $V(\phi, \sigma)$ describing a slowly rolling field tunneling to a minimum at the origin at an approximately constant rate.
• Figure 2: Schematic illustration of the PBH mass spectrum from vacuum bubbles with an intermediate matter-dominated era.
• Figure 3: [Left] Allowed normalization range for a PBH mass function $\propto M^{-1/2}$ to be consistent with the HSC candidate event reported after 7 hours of observations Niikura:2017zjd. The HSC constraint (shaded blue) takes into account the updated finite-source size effects Smyth:2019whbSugiyama:2019dgt. Thick purple line represents the best fit and the band corresponds to a 95% confidence level (CL) interval. For each line in the allowed range, the mass function can be made consistent with $f_{\rm{PBH}}=1$ by introducing a low-mass cutoff in the $10^{-15}-10^{-10}M_\odot$ range. [Middle] Green line shows a model mass function, in which PBHs can account for HSC and OGLE microlensing observation, LIGO observations Sasaki:2016jop (this region will be further tested with stochastic gravity-wave background Wang:2016anaNakamura:1997sm) and seeds of supermassive black holes. After 6 hours of additional observation by HSC, we can exclude $f_{\rm PBH}=1$ normalization (red region), assuming null detection in future observation. [Right] Green line shows the most pessimistic scenario, corresponding to the lowest possible normalization and $M_{\rm min} \sim 10^{-16}M_\odot$, for which PBH can still account for all of the DM. The red region is the exclusion region of normalization $f_{\rm PBH}$ at a given $M_{\rm min}$, assuming 88 hours of new observation and null detection. The blue region in each panel is the constraint assuming monotonic mass function and corresponding observation time (7, 7$+$6, and 88 hours from left to right). Constraints from extragalactic $\gamma$-rays from BH evaporation Carr:2009jm (additional constraints in this region due to positron production from BH evaporation have been also recently suggested Dasgupta:2019caeLaha:2019ssqDeRocco:2019fjq), microlensing Kepler data Griest:2013aaa, MACHO, EROS and OGLE microlensing Tisserand:2006zx, and the accretion effects on the CMB observables Ali-Haimoud:2016mbv (see also Ref. Poulin:2017bwe) are also displayed. The label of $(\delta)$ denotes that the constraint is derived assuming monotonic mass function.