Primordial black hole detection through diffractive microlensing

TL;DR

This paper proposes using diffractive microlensing of distant quasars at infrared to submillimeter wavelengths to detect sub-lunar primordial black holes, leveraging wave optics features to determine their mass and abundance.

Contribution

It introduces a novel observational method employing wave optics in microlensing to directly measure the mass and distribution of sub-lunar primordial black holes.

Findings

Estimated microlensing optical depth for sub-lunar PBHs.

Predicted event rate of 0.1 to 0.3 per year per quasar.

Proposed long-term quasar survey to detect wave optics features.

Abstract

Recent observations of gravitational waves motivate investigations for the existence of Primordial Black Holes (PBHs). We propose the observation of gravitational microlensing of distant quasars for the range of infrared to the submillimeter wavelengths by sub-lunar PBHs as lenses. The advantage of observations in the longer wavelengths, comparable to the Schwarzschild radius of the lens (i.e. $R_{\rm sch}\simeq \lambda$) is the detection of the wave optics features of the gravitational microlensing. The observation of diffraction pattern in the microlensing light curve of a quasar can break the degeneracy between the lens parameters and determine directly the lens mass as well as the distance of the lens from the observer. We estimate the wave optics optical-depth, also calculate the rate of $\sim 0.1$ to $\sim 0.3$ event per year per a quasar, assuming that hundred percent of dark matter is made of sub-lunar PBHs. Also, we propose a long-term survey of quasars with the cadence of almost one hour to few days to resolve the wave optics features of the light curves to discover PBHs and determine the fraction of dark matter made of sub-lunar PBHs as well as their mass function.