Strong lensing constraints on primordial black holes as a dark matter candidate

Dark matter could comprise, at least in part, primordial black holes (PBH). To test this hypothesis, we present an approach to constrain the PBH mass ($M_{\mathrm{P}\mathrm{B}\mathrm{H}}$) and mass fraction ($f_{\mathrm{P}\mathrm{B}\mathrm{H}}$) from the flux ratios of quadruply imaged quasars. Our approach uses an approximate Bayesian computation (ABC) forward modeling technique to directly sample the posterior distribution of $M_{\mathrm{P}\mathrm{B}\mathrm{H}}$ and $f_{\mathrm{P}\mathrm{B}\mathrm{H}}$, while marginalizing over the subhalo mass function amplitude, spatial distribution, and the size of the lensed source. We apply our method to 11 quadruply-imaged quasars and derive a new constraint on the intermediate-mass area of PBH parameter space ${10}^4$M${}_{\odot }<M_{\mathrm{P}\mathrm{B}\mathrm{H}}<{10}^6$M${}_{\odot }$. We obtain an upper limit $f_{\mathrm{P}\mathrm{B}\mathrm{H}}<0.17$ (95% C.L.). This constraint is independent of all other previously published limits.