Planck constraint on relic primordial black holes

We investigate constraints on the abundance of primordial black holes (PBHs) in the mass range 10(15)-10(17) g using data from the cosmic microwave background (CMB) and McV extragalactic gamma-ray background (EGB). Hawking radiation from PBHs with lifetime greater than the age of the Universe leaves an imprint on the CMB through modification of the ionization history and the damping of CMB anisotropies. Using a model for redshift-dependent energy injection efficiencies, we show that a combination of temperature and polarization data from Planck provides the strongest constraint on the abundance of PBHs for masses similar to 10(15)-10(16) g, while the EGB dominates for masses greater than or similar to 10(16) g. Both the CMB and EGB now rule out PBHs as the dominant component of dark matter for masses similar to 10(16)-10(17) g. Planned McV gamma- ray observatories are ideal for further improving constraints on PBHs in this mass range.